key: cord-0068342-41pf848f
authors: Yang, Hongcheng; Zhang, Shuren; Yang, Hongyu; Wen, Qingyu; Yang, Qiu; Gui, Ling; Zhao, Qian; Li, Enzhu
title: The latest process and challenges of microwave dielectric ceramics based on pseudo phase diagrams
date: 2021-10-11
journal: J Adv Ceram
DOI: 10.1007/s40145-021-0528-4
sha: a919d8a59f2203065155695454fa66db97ac6333
doc_id: 68342
cord_uid: 41pf848f

The explosive process of 5G communication evokes the urgent demand of miniaturized and integrated dielectric ceramics filter. It is a pressing need to advance the development of dielectric ceramics utilization of emerging technology to design new materials and understand the polarization mechanism. This review provides the summary of the study of microwave dielectric ceramics (MWDCs) sintered higher than 1000 from 2010 up to now, °C with the purpose of taking a broad and historical view of these ceramics and illustrating research directions. To date, researchers endeavor to explain the structure-property relationship of ceramics with multitude of approaches and design a new formula or strategy to obtain excellent microwave dielectric properties. There are variety of factors that impact the permittivity, dielectric loss, and temperature stability of dielectric materials, covering intrinsic and extrinsic factors. Many of these factors are often intertwined, which can complicate new dielectric material discovery and the mechanism investigation. Because of the various ceramics systems, pseudo phase diagram was used to classify the dielectric materials based on the composition. In this review, the ceramics were firstly divided into ternary systems, and then brief description of the experimental probes and complementary theoretical methods that have been used to discern the intrinsic polarization mechanisms and the origin of intrinsic loss was mentioned. Finally, some perspectives on the future outlook for high-temperature MWDCs were offered based on the synthesis method, characterization techniques, and significant theory developments.

Over the past half century, semiconductor integration the huge amount and a wide variety of components with different functions are passive devices. The core materials of these components are various types of functional ceramic materials. Microwave dielectric ceramics (MWDCs) are the pivotal component of a passive device, which are mainly used as filters, resonators, RF antennae, frequency discriminators in electronic countermeasures, navigation, radar, home satellite live television receivers, and hand-held mobile phones. The applications of MWDCs in different frequency are directly plotted in Fig. 1 . However, the development of microwave ceramics had gone through a sluggish procession because of the lack of suitable materials for dielectric resonator. The discovery of rutile (also known as titanium dioxide ceramics) in the 1970s makes it possible to synthesis dielectric resonator [1] . Various literature has been reported to explore the potential candidates of MWDCs after that, from single oxide, binary oxide, to ternary oxide. According to the data in the Web of Science, over 1000 papers were published about MWDCs around the world after 2000. Figure 2 presents the trend of published papers where more than 30% of investigations belong to China.

To evaluate the dielectric properties of ceramics, the relative permittivity (ε r ), dielectric loss (loss tangent or quality factor (Q×f value)), and temperature coefficient of resonant frequency (τ f ) are the three pivotal characteristics. As early as in 2006, the direction of development of microwave dielectric materials has been highlighted by Ohsato et al. [2] , including high Q and low ε r ceramics for millimeter-wave application, high Q and high ε r ceramics for base station, and high ε r ceramics for miniaturization of mobile phone. Up to now, researchers have explored hundreds of ceramics to enrich the database of MWDCs, but only a dozen of those ceramics with unique properties have been commercially used to fabricate relevant devices because most of the ceramics lack stability or generate large loss in the electronic components. Booming development of millimeter technology and 5G communication have rendered a new round of requirement of MWDCs of low permittivity with a stable dielectric loss in the scope of frequency up to 100 GHz. Especially, the emergency of COVID-19 makes video conferencing and telecommuting as a daily part in our lives. Consequently, the unprecedented growth of global data volume and huge demand for high data rates urge researchers to search more alternative materials for commercial electronic market. It is also a very significant issue for the industry to yield ceramics with ultra-low permittivity which are suitable for 5G and 6G communication system. However, it is still a "try and error" state in our experiments for discovering materials or optimizing the properties of the reported ceramics. The main difficulty in the development of MWDCs is to understand the fundamental relationship of compositionstructure-property and draw general trends throughout the field, after normalizing and comparing the various results. Despite long-term sustained attempts, there is no systematic or comprehensive theory which can provide common guidance in the experiments and drive currently reported ceramics toward commercialization applications.

With the exploration of MWDCs clusters and the development of modern experiment techniques, investigations about MWDCs have been largely scoped by the designs and search for new systems and reoptimizing their properties. It is paramount that an MWDCs candidate has an appropriate dielectric constant, low dielectric loss, and near-zero temperature coefficient of resonant frequency for applications. Generally, to tune the microwave dielectric properties, there are two parts that should be taken into consideration (extrinsic and intrinsic parts). Extrinsic part is usually regarded as the influence originated from the synthesis method and raw materials. MWDCs usually prepare by solid state reaction method, and the sintering conditions directly influence the microstructure and compactness of ceramics, which subsequently affect the microwave dielectric properties. Meanwhile, the selectivity of size distribution, purity, non-stoichiometric ratio, species of different compounds, and pretreatment of raw materials based on their physical and chemical properties are crucial for reaching optimal microwave dielectric properties. For example, the procedures to reduce pores are designed for ceramics containing the volatile element, evolving non-stoichiometric ratio in the chemical formula, and providing the compensation atmosphere of volatile element. The relevant attempts are mostly discussed for the rock salt structure ceramics such as Li 2 Mg 3 TiO 6 . Besides, various synthesis methods, namely sol-gel method, sink plasma sintering method, and high energy ball-milling method are gradually used for preparing the MWDCs, and numbers of studies analyze the discrepancy of microwave dielectric properties obtained with different methods. The intrinsic part stems from anharmonic lattice vibration, which primarily generates large dielectric loss. As yet, there is no technology or theory that could feasibly adjust the anharmonic lattice vibration to reduce dielectric loss. In the experiment, after carefully controlling the sintering conditions and selecting raw materials, the most pragmatic approach to optimize the properties is cation substitution with the consideration of the radii and the electronegativity of cations, contributing to reducing the dielectric loss or modifying the temperature coefficient of resonant frequency. Near-zero temperature coefficient of resonant frequency is also obtained by designing co-exited phase system with introduction of two ceramics with opposite τ f values, but the composite ceramics may lead to a poor Q×f value. More recently, the strategy of tri-layer structures of Zn 1.01 Nb 2 O 6 /TiO 2 /Zn 1.01 Nb 2 O 6 [3] , MgTiO 3 /TiO 2 /MgTiO 3 [4] , and Zn 3 Nb 2 O 8 /TiO 2 / Zn 3 Nb 2 O 8 [5] were verified as a method to obtain the temperature-stable ceramics with low dielectric loss.

Currently, the database of MWDCs is enriched by insightful information about the structure and properties, and the growing number of literature converts from description of phenomena to explanation of the theoretical mechanism of the dielectric materials. Thorough and comprehensive investigation of ceramics is gradually presented to estimate the extrinsic and intrinsic influence on the microwave dielectric properties. For instance, the common discussion of polarization mechanism is usually based on the ionic polarization, where the Clausius-Mossotti (C-M) equation is applied to evaluate the discrepancy of theoretical ε r and measured ε r . The popularization of Rietveld-refinement in the literature supports the analysis of lattice parameters, packing fraction, and chemical bond characteristic obtained by the complex chemical bond theory (P-V-L) theory. Especially, disassembling the crystal into the sum of sample binary compound based on the crystal parameters and coordinate numbers of each ions [6] , the investigations about application of P-V-L theory into multi-type structure emerge in abundance. The origin of dielectric loss is quantified by lattice vibrational spectroscopy, and the contribution of each chemical bond to the microwave dielectric properties is verified by P-V-L theory. For some unique ceramics, researchers bend themselves to exploring the underlying mechanism for the observed phenomenon. The influence of long-range movement of charged defects in the grain and grain boundary was estimated by the impedance analysis, terahertz (THz) time-domain spectroscopy analysis, and the electron paramagnetic resonance spectra, which can explain the defect generation mechanism in doped Li 2 ZnTi 3 O 8 ceramics. The analysis of disordered-ordered crystal structure evolution and super-lattice in rock salt ceramics and complex perovskite ceramics gives evidence to explain the ultra-low dielectric loss. Both the development of experimental and theoretical method allows us to summarize the relevant experimental probes of different systems and propose the challenges and prospects of MWDCs.

While many great review and perspective articles have been published about MWDCs, they have finished the review by classified MWDCs based on the criteria of sintering temperature, dielectric constant, and crystal structure [1, [7] [8] [9] . Furthermore, the early works before 2010 are mainly concentrated on the description of phase composition, micrographic images, and variation of microwave dielectric properties. The topic about the MWDCs sintered lower than 950 is ℃ especially focused owing to the advantages of low-temperature co-fired ceramics (LTCC) technology where this approach guarantees the integration of electronic components. Considering either the timespan or topic covered, the mentioned ceramics, in this review, are all sintered higher than 1000 . The ℃ LTCC system including ceramics with a few sintering aids, glass-ceramics system, or glass-free system is not referred. To follow the development of new analysis methods, MWDCs, beginning with the first reported properties and upgrading the relevant references after 2010, were included. Additionally, because of so various structures and properties of MWDCs, pseudo phase diagram was used to classify the ceramics according to the composition, which will serve as the basis and link for each pseudo phase diagram of diversity composition. The organization of this review consists of a brief section detailing the phase evolution or structure transformation of oxide ceramics in the designed pseudo phase diagram, and then the chronological experimental probes for a unique system are summarized.

The phase diagram is a visual representation of the phase equilibrium, which defines the composition of multiphase system. It is an efficient and convenient technique to analyze the composition and their proportion, which plays a significant role in guiding the research and exploration of materials to reduce the manpower and material resources effectively. This section provides a broad context by summarizing the ceramics system based on pseudo phase diagram, and all the composition in the following pseudo phase diagram is in molar ratio. The endpoint of each pseudo phase diagram contains more than one component, and the labelled ceramics are the primary system reported by researchers. The summary of investigations in the same general formal is listed in detail.

There is a low ε r (< 10) for silicates, owing to the low ionic polarizability of Si 4+ and half covalent bond in Si-O. In the binary silicate, the CaSiO 3 , Mg 2 SiO 4 , Zn 2 SiO 4 , and Re 2 SiO 5 are the main representatives, where CaSiO 3 usually appeared as the crystalized phase in CaO-B 2 O 3 -SiO 2 glass. Ternary silicate such as diopside-type CaMgSi 2 O 6 , melitile-type A 2 BC 2 O 7 and AB 2 C 2 O 7 (A = Sr, Ca, Ba; B = Mg, Zn, Co, Mn, Cu), and cuspidine-type Ca 3 SnSi 2 O 9 were highlighted by researchers, due to the diverse crystal structures in those systems. With the wake of exploration of new ceramics, the germanate gradually occurred as a candidate material with low dielectric loss despite of the expensive cost of GeO 2 as raw material. The pseudo phase diagram of the silicate and germanate is presented in Fig. 3 , where the primary phases of binary and ternary silicate and germanate are listed in the phase diagram.

Synthesis of dense SiO 2 ceramic is challengeable because of its complexity in polymorphs and phase transitions. Until 2012, microwave dielectric properties of SiO 2 ceramic were reported as ε r ≈ 3. 81 [48, 49] .

The unpresented ternary silicate and germanate phase in pseudo phase diagrams are summarized as well in this section. The rare earth-based ternary silicate oxides, such as apatite with general formula A 10 (MO 4 ) 6 O 2 (A = alkaline earth, rare earth, Pb; M = Si, Ge, P, V), have received much attention since the apatite structure allowed numbers of substitutions at all the three sites. The lattice parameters and the local charge compensation of apatite type compounds were determined in 1972 [50] , and those ceramics were established as candidate of fluorescent lamp phosphors and laser technology. To improve the densification of lithium apatite LiRe 9 (SiO 4 ) 6 O 2 ceramics (Re = La, Pr, Nd, Sm, Eu, Gd, Er), relative density was higher than 90% for all samples after doping 1 wt% LiF [51] . The microwave dielectric properties of SrRE 4 Si 3 O 13 (RE = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er, Tm, Yb, and Y) were in the range of 9-16 for permittivity with the maximum of Q×f value ≈ 26,000 GHz [52] , while the optimal microwave dielectric properties of CaRE 4 Si 3 O 13 (RE = La, Nd, Sm, and Er) were ε r ≈ 13.37, Q×f value ≈ 18,600 GHz, and τ f ≈ -17.8 ppm/ at Re = Er [53] .

℃ To obtain new dielectric materials, some researchers pursued materials with the composition containing GeO 2 and Ga 2 O 3 and reported microwave dielectric properties of those materials firstly. With inverse spinel structure, LiGa 5 O 8 was verified as a cubic structure where Li + and Ga 3+ distributed in the octahedral B site with 1:3 ordering [54] . The large deviation between ε r and ε rth in Ba 2 MGa 11 O 20 (M = Bi, La) was ascribed to the "rattling" effect of cations and the existence of lone pair ions of Bi 3+ [55] . The different τ f values of AGe 4 O 9 (A = Ba, Sr) were ascribed to the distortion of [GeO 6 ] octahedron where τ f values were -44.2 ppm/ ℃ for the former and -11.7 ppm/ for the later [56] . ℃ Normal garnet A 3 Y 2 Ge 3 O 12 (A = Ca, Mg) ceramics possessed τ f ≈ 120.5 ppm/ for A = Ca and ℃ -40.6 ppm/ ℃ for A = Mg [57] . As doped ions, (Li 0.5 Ga 0.5 ) 3+ in Mg 2 Al 4 Si 5 O 18 would obtain the highest Q×f value of 50,560 GHz [58] . Ca 3 M 2 Si 3 O 12 (M = Yb, Y) ceramics were consistent with the general formula of garnet structure, and those ceramics crystalized as silico-carnotite structure with high-energy ball milling method [59] . The microwave dielectric properties were recorded as ε r ≈ 9. [60] [61] [62] . Similarly, Sr 3 B 2 Ge 3 O 12 (B = Yb, Ho) were investigated by Li et al. [63] using vibration spectroscopy, and the τ f was tuned to near zero with CaTiO 3 ceramics. 0.8Y 3 MgAl 3 SiO 12 -0.2TiO 2 ceramic sintered at 1475 ℃ showed a τ f ≈ +5.2 ppm/ , where ℃ the co-existed phase contained Y 2 Ti 2 O 7 and TiO 2 along with Y 3 MgAl 3 SiO 12 phase [64] . Dense Mg 3 Ga 2 GeO 8 ceramics presented microwave dielectric properties of ε r ≈ 9.41, Q×f value ≈ 133,113 GHz, and τ f ≈ -63.54 ppm/ [65] . Single phase LiYSiO ℃ 4 ceramics could be obtained in 1100-1140

, and a near ℃

-zero τ f of (+4.52)-(+8.03) ppm/ was observed [66] . ℃ Furthermore, phase transition from A2/a to P2 1 /a was observed in new silicate in the formula of CaSn 1-x Ti x SiO 5 , where the variation of τ f values was ascribed to the Sn/TiO 6 octahedral distortion [67] . Secondary phase of SnO 2 and SrSiO 3 appeared at 0.2 ≤ x ≤ 0.45 in Ca 1-x Sr x SnSiO 5 ceramics, which could adjust the positive τ f of CaSnSiO 5 to -1.2 ppm/℃ [68] . CaSiO 3 and CaSnSiO 5 phases would improve the τ f to -7.2 ppm/ in Ca ℃ 2 (Hf 1-x Sn x )Si 4 O 12 when x = 0.4 [69] .

There is a large body of niobate and tantalate dielectric ceramics, and the relevant researches highlight the phase evolution, structure transformation, and chemical www.springer.com/journal/40145 bond characteristics. In order to elucidate the influence of undercoordinated sites on the dielectric properties, analysis according to P-V-L theory and vibration spectra is verified as valid approach to understand the relationship of the state of chemical bond with polarization and stability of lattice. Indeed, it seems that researchers could identify the contribution of each chemical bond to dielectric properties by P-V-L theory and infrared reflectivity spectrum. However, reaching general conclusions about the effect of a unique chemical bond or Wycoff site on different properties may be difficult, since the P-V-L theory is just predictable theoretically. The actual dielectric properties of ceramics are still evaluated based on experiments, and thorough, quantitative, and multiperspective analysis is required. Figure 4 is the phase diagram of the mainly reported niobate and tantalate dielectric ceramics, where the rutile-type, ixiolitetype, and columbite-type structures were obtained after (Zn 1/3 Nb 2/3 ) 4+ was doped into TiO 2 . The detailed phase division of A 0.5 B 0.5 CO 4 and the relevant investigations of this binary system are summarized in the following.

Rutile, brookite, and anatase are the three types of TiO 2 in nature. TiO 2 itself possesses a high permittivity ≈ 100, a low dielectric loss tangent (tanσ) value (6×10 -5 at a frequency of 3 GHz), and a high τ f value of 450 ppm/ [70] . It is valid that TiO ℃ 2 phase is used to target the aim of near zero τ f value as a secondary phase in the system with a negative τ f value. Meanwhile, long-term focus has been paid on the structure transformation and property optimization of TiO 2 with substitution ions of different physicochemical properties. The cation substitution for Ti 4+ can reduce the dielectric loss or tune the τ f value, evolving monovalent, divalent, trivalent, tetravalent, or pentavalent cations, and their groups of two cations. Especially, the extensive elaboration of dependence of microwave dielectric properties on the crystal structure of (Zn 1/3 B 5 2 + /3 ) x Ti 1-x O 2 (B 5+ = Nb, Ta) ceramics was reported by Kim and Kang [71] . The phase relation of ternary system of ZnO-TiO 2 -Nb 2 O 5 was first discussed in 1992 [72] . It summarized that the solid solution of rutile phase appeared in the range of molar content of (Zn 1/3 Nb 2/3 ) 4+ lower than 58%, ixiolite ZnTiNb 2 O 8 exited in the range of 69%-85%, while columbite solid solution of ZnNb 2 O 6 formed when the content was higher than 93% [73] , and the solid solution area of different types was marked with shadow in the pseudo phase diagram in Fig. 4 [78] , where the expansion of bond length and cell volume renders the decline of covalency of all bonds. The decline of bond ionicity was obtained since the shrinking of cell volume and bond length in Zn 0.15 Nb 0.3-x Ta x TiZr 0.55 O 2 [79] .

The structure of formula A 0.5 B 0.5 CO 4 can be categorized into four types: wolframite-type www.springer.com/journal/40145 (ε r ≈ 26, Q×f value ≈ 120,816 GHz, and τ f ≈ -50.2 ppm/ , ℃ at f = 6.85 GHz [86] ). The microwave dielectric properties of wolframite-type AZrB 2 O 8 (A = Mn, Zn, Mg, Co, Ni; B = Nb, Ta) and the structure-relationship were determined via combining the far-infrared and terahertz spectroscopy with P-V-L theory [87] [88] [89] [90] [91] . Partial replace of A-site (such as Mg 0.5 Zn 0.5 ZrNb 2 O 8 [92] , Zn 1-x Co x ZrNb 2 O 8 [93] [94] [95] ), Zr-site substitution of Zn(Ti 1-x Zr x )Ta 2 O 8 [96] , ZnZr 1-x Sn x Nb 2 O 8 [97, 98] , doped Nb-site of MgZr(Nb 1-x Sb x ) 2 O 8 [99, 100] , ZnZrNbTaO 8 [101] , MgZrNb 2-x (Sn 1/2 W 1/2 ) x O 8 [102] , and nonstoichiometric MgZrNb 2+x O 8+2.5x [103] provided evidence that relative density, packing fraction, bond valence, and chemical bond characteristics majored the variation of microwave dielectric properties. To adjust the negative τ f values, the study about the relationship of TiO 2 on MgZrNb 2 O 8 [104] and ZnZrNb 2 O 8 [105] presented that co-exited ceramics would reach near zero τ f values. The microwave dielectric properties were ε r ≈ 43, Q×f value ≈ 46,110 GHz, and τ f ≈ -2.5 ppm/ for 0.63MgZrNb [109, 110] . The characteristic of rutile Co 0.5 Ti 0.5 NbO 4 was sought by solid state reaction and sol-gel method [111, 112] , where the microwave dielectric properties were ε r ≈ 64, Q×f value ≈ 65,300 GHz, τ f ≈ 223.2 ppm/ and ℃ ε r ≈ 64.19, Q×f value ≈ 16,800 GHz, τ f ≈ 66.17 ppm/ , ℃ respectively. In the solid solution of Ni 0.5-x Zn x Ti 0.5 NbO 4 , the dielectric constant was enhanced from 56.8 to 62.54 [113] . Introduction of CoNb 2 O 6 and Zn 1.01 Nb 2 O 6 into CoTiNb 2 O 8 rendered the Q×f increasing considerably due to the enhanced densification and obtained the τ f values of 0.5 and 0 ppm/ , respectively [114, 115] . ℃ Zhang et al. [116] and Li et al. [117] reported that τ f value would shift from positive to negative after Zr substitution in CoTi 1-x Zr x Nb 2 O 8 , where the τ f value was correlated with oxygen octahedral distortion and B-site bond valence. Superlattice diffraction peak which is relevant with cation ordering was observed in Co 0.5 Ti 0.5 Nb 1-x Sb x O 4 ceramics, contributing to the augment of Q×f value [118] .

The trirutile-type structure was observed in some tantalates, antimonates, and bismuthates. This crystal structure was built by ordering octahedral cations along c-axis, which possessed three times c-axis of rutile-type one [119, 120] . Currently, Co 0.5 Ti 0.5 TaO 4 [121] , NiTiTa 2 O 8 [122] , Co 0.5 Zr 0.5 TaO 4 [90] , NiSnTa 2 O 8 [123] were reported as trirutile-type structure. Among them, NiSnTa 2 O 8 showed a near zero τ f value (ε r ≈ 21.04, Q×f value ≈ 31,328 GHz, and τ f ≈ -2.63 ppm/ ). ℃ Ixiolite phase ZnTiNb 2 O 8 is a fully disordered α-PbO 2 structure, where Zn/Ti/Nb ions statistically occupied the octahedral cation sites [124] . Up to now, numbers of substitution on ZnTiNb 2 O 8 have been reported, such as Co [125] , Mg [74] , Ca [126] , Sn [127] , Zr [128] , and Ta [129] [130] [131] . The crystal structure refinement and Raman spectrum study of ZnTiNb 2 O 8 , together with the mode assignment were completed by Liao and Li [132] . In the ZnO-Nb 2 O 5 -xTiO 2 (1 ≤ x ≤ 2) system, ceramics were composed of Zn 0.17 Nb 0.33 Ti 0.5 O 2 and ZnTiNb 2 O 8 when x ≥ 1.8 [133] . Using the effective route of sintering reaction for ZnNb 2 O 6 and TiO 2 nano powders, a superior property of ZnTiNb 2 O 8 was achieved compared with that prepared by solid-state method [134] . Dielectric constant and dielectric loss were evaluated in microwave and THz range in Al 0.5 Nb 0.5 doped into ZnTiNb 2 O 8 , where the results indicated the negligible shift of dielectric constant in those frequencies, as shown in Fig. 6 [135] . Furthermore, ixiolite MgTiNb 2 O 8 prepared by aqueous sol-gel process and then sintered at 1000 showed ℃ ε r ≈ 33.8, Q×f value ≈ 26,260 GHz, and τ f ≈ -19.2 ppm/ [136] .

℃ In the family of AB 2 O 6 (A = Ca, Mg, Mn, Co, Ni, Zn; B = Ta, Nb), the relationship of permittivity with electronegativity was presented by Lee et al. [137] . Two structure classifications have been identified in this system, namely rutile-type (trirutile) and α-PbO 2type (tri-α-PbO 2 , columibite) [138, 139] . Comprehensive studies of columbite niobates concluded that the ε r was in the range of 17-22, τ f value varied from -45 to -76, [140, 141] . The investigations about property optimization and preparation methods were concentrated on MgNb 2 O 6 , ZnNb 2 O 6 , and ZnTa 2 O 6 due to their potential of application. For sintering behavior, the sintering temperature can be reduced to 1150 of ℃ MgNb 2 O 6 by sol-gel method [142] . Doped ceramics of (Zn 1-x Ni x )Ta 2 O 6 [143] , Zn(Ta 1-x Nb x ) 2 O 6 [144] , Zn(Ta 1-x Sb x ) 2 O 6 [145] , and composite ceramics composed of ZnO-

and (1-x)ZnTa 2 O 6 -xNiNb 2 O 6 were designed successfully to reach near-zero τ f value [146] [147] [148] [149] . Liu and Deng [150] proposed that the grain size of ZnNb 2 O 6 -(Zn 0.7 Mg 0.3 )TiO 3 ceramics became smaller with the ZnNb 2 O 6 content increasing. The secondary ZnV 2 O 6 was observed with higher than 1 wt% V 2 O 5 into ZnNb 2 O 6 [151] . The property comparison of MgTa 2 O 6 was obtained by sol-gel procession and solid reaction sintering by Wu et al. [152] . Liu et al. [153] verified that the unpaired d-electrons contribution to the room temperature loss should be taken into consideration of ZrTiO 4 -ZnNb 2 O 6 . It was interesting that the structure transformation was identified as tri-α-PbO 2 , α-PbO 2 , trirutile, and rutile in (1-x)ZnTa 2 O 6 -xTiO 2 along with the increase of x [154] . ZnNb 2 O 6 ceramics prepared by microwave sintering exhibited relative density of 94.3%, and the quality factor was dominated by the distribution of grain size [155] . Recently, the intrinsic dielectric properties were investigated using chemical bond theory and lattice vibrational spectra, which indicated that B 1u mode at 168.87 cm -1 was highly related to the dielectric properties [156] , and the fitted results of infrared-related spectrum are presented in Fig. 7 . 

The crystal structure of double tantalates of rare-earth elements with titanium tantalite compounds based on ReTiTaO 6 is sorted into two parts: orthorhombic aeschynite symmetry with rare earth atomic number in the range of 55-66 and orthorhombic euxenite symmetry with that of 67-71 [157, 158] . Generally, high ε r and positive τ f were obtained for the former, while relatively low ε r and negative τ f were observed for the latter. The effect of microstructure on properties of RETiNbO 6 (RE = La, Sm, and Y) ceramics was presented by Lei et al. [159] . The dielectric constant of RETiNbO 6 system (RE = Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Y, and Yb) and RETiTaO 6 (RE = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y, Er, Yb, Al, and In) increases with the RE ionic radius [157, 158] . It was reported that LaTiNbO 6 usually stabilized as a monoclinic structure, and Zhang and Zuo [160] proposed that ceramics with coexistence of O and M phases could be achieved after prolonging the annealing time. And then, they [161] [162] [163] [164] conducted out the substitutions for La and Nb sites, in which the structure evolution, octahedral distortion, and vibrational spectrum were elaborated in detail. More recently, dielectric and optical properties of Ln 0.8 Lu 0.2 TiNbO 6 (Ln = Ce, Pr, Nd, and Sm) were presented by John and Solomon [165] , where the optimal microwave dielectric properties were shown for Sm 0. 8 [167] [168] [169] [170] [171] [172] [173] [174] [175] , and Nb site by Ta, Sb [176] [177] [178] [179] were completed to adjust the microwave dielectric properties. In our recent reports, the groups of different isovalent cations of (A x B 1-x ) 5+ (A = Mg, Al, Si, Zr; B = W, Mo) have been listed as valid substitution for Nb site to reduce dielectric loss [180] [181] [182] [183] . The analysis of combination of P-V-L theory and vibration spectrum suggested that doping into Nb site was beneficial to improving quality factor. Meanwhile, NdNbO 4 prepared in sol-gel method or composite ceramics composed of NdNbO 4 -CaTiO 3 [184] , NdNbO 4 -CaF 2 [185] , and NdNbO 4 -MgO [186] have also been reported to perfect the properties. Similarly, intrinsic dielectric properties of EuNbO 4 were studied by Liu et al. [187] . In the full range of La 2 O 3 -Nb 2 O 5 -V 2 O 5 system, four typical phase regions were verified, including monoclinic fergusonite, tetragonal sheelite, B-site ordered sheelite, and composite of monoclinic LaVO 4 and tetragonal sheelite phases [188] .

Likewise, MgO was designed as an addition for LaNbO 4 ceramics and the excellent properties were listed as ε r ≈ 19.8, Q×f value ≈ 94,440 GHz, and τ f ≈ 6.1 ppm/ [189] . More recently, structure ℃ -property relationship of another A 3+ B 5+ O 4 binary oxide, zircontype AVO 4 (A = Eu, Y) ceramics, was discussed by packing fraction and bond valence [190] . Ferroelastic phase transition from monoclinic fergusonite to tetragonal scheelite was observed by in situ Raman spectroscopy and X-ray diffraction of La(Nb 0.9 V 0.1 )O 4 , and the schematic of ε r typical-ceramics versus temperature was shown by Zhou et al. [191] . NiO/CoO added into LaNbO 4 would distinctly optimize the quality factor since the larger and uniform grain was obtained [192] . Although the thermal properties [193] [194] [195] [196] and the first-principles calculation of electronic structure and optic properties of RETaO 4 (RE = Y, La, Sm, Eu, Dy, Er) [197] have been investigated, the intrinsic dielectric loss has not been summarized in this system. Microwave dielectric properties of ErNbO 4 prepared by sol-gel method were reported by Devesa et al. [198] , and the grain size varied from 31.27 to 86.65 µm and 40.96 to 78.23 µm by Rietveld refinement and Sherrer's formula, respectively. ZrTiO 4 followed the general formula of ABO 4 , and the intrinsic dielectric loss of Zr 0.8 Sn 0.2 TiO 4 was investigated by THz time domain spectroscopy [199] .

The structure of corundum-like phase of Mg 4 Nb 2 O 9 was verified by Kumada et al. [200] , where the cations were ordered by the stack of two layers of a mixture of Mg and Nb and one layer of Mg along the c-axis. Mg 4 (Nb 2-x Ta x )O 9 solid solution was synthesized in the sintering temperature range of 1350-1400 [201] , ℃ which possesses a comparable quality factor (Q×f value ≈ 350,000 GHz for x = 2) to that of Al 2 O 3 . To deal with the limitation of high sintering temperature, both Mg 4 Nb 2 O 9 and Mg 4 Ta 2 O 9 were generated by sol-gel method and the variation of property with www.springer.com/journal/40145 sintering temperature was analyzed [202] [203] [204] [206, 207] , which presented that the appearance of Mg 4 Nb 2 O 9 pure phase was more easily with Mg(OH) 2 as raw materials. A dramatically improvement of quality factor was achieved by Ni and Ta co-doped into this system, and (Mg 0.95 Ni 0.05 ) 4 (Nb 1-x Ta x ) 2 O 9 shows satisfied properties of ε r ≈ 12.76, Q×f value ≈ 442,000 GHz, and τ f ≈ -54 ppm/ , when ℃ x = 1 and sintered at 1375 [208] . 5+ substitution at Nb 5+ site (B = Li, Mg, Al, Ti) in Mg 4 Nb 2 O 9 -based ceramics revealed that the τ f depended on the distortion of the oxygen octahedra, while (Ti 1/2 W 1/2 ) 5+ substitution had the highest quality factor of 233,000 GHz [209] . The investigation of y(Mg 0.95 Co 0.05 ) 4 Ta 2 O 9 -(1-y)CaTiO 3 ceramics provided a promising dielectric material for application with temperature stability, and the properties were shown as ε r ≈ 25.78, Q×f value ≈ 200,000 GHz, and τ f ≈ -4.69 ppm/ [210] . ℃ Zn 3 Nb 2 O 8 was another promising binary niobite compound, which could be successfully produced with 98% theoretical density sintered at 1100 [211] . A ℃ two-stage sintering method was proposed to optimize the microstructure of Zn 3 Nb 2 O 8 [212] , where the sintering temperatures were 1150 and 1200 for the ℃ first time and the second sintering temperatures were 1050 and 1100 , respectively. Sintered based on this ℃ approach, ceramics presented denser grain packing and less abnormal grain growth. Adding secondary phase into ceramics to compensate for τ f value would introduce a large amount of second phase, which were ascribed to the large dielectric loss. Aiming to reduce the defects stemmed from the secondary phase, layercofired ceramic architectures were designed such as Zn 1.01 Nb 2 O 6 /TiO 2 /Zn 1.01 Nb 2 O 6 [3] , MgTiO 3 /TiO 2 /MgTiO 3 [4] , and Zn 3 Nb 2 O 8 /TiO 2 /Zn 3 Nb 2 O 8 [5] . High-Q value was remained and temperature-stable MWDCs were obtained for all the reported tri-layer co-fired ceramics.

Closely followed by the ever-growing explosion of global data volume and the rapid boost of millimeterwave technology, the requirement of materials with low permittivity (ε r ≤ 25) and high Q×f value is increasingly urgent. In the exploration of new composition ceramics, many rock-salt Li-containing compounds emerge as focal points. The general formula of rock-salt ceramics is A a B b O a+b (A + = Li, Na; B 4+ = Ti, Sn, Zr; B 5+ = Nb and Ta). Li 2 TiO 3 underwent an order-disorder phase transition at 1213 , in which ℃ the structure consisted of ordered (Li,Ti) layer, with the property of ε r ≈ 12.76, Q×f value ≈ 44,200 GHz, and τ f ≈ -54 ppm/ [213] . The sintering behavior of ℃ excess Li for non-stoichiometry Li 2+x TiO 3 ceramics was investigated by Bian and Dong [214] and Hao et al. [215] after the determination of pseudo-binary of Li 2 O-TiO 2 [216, 217] . For co-doped substitution, Zn 1/3 Nb 2/3 , Mg 1/3 Nb 2/3 , and Co 1/3 Nb 2/3 addition into Li 2 TiO 3 could adjust the τ f from positive to negative [218] [219] [220] . Cu 1/3 Nb 2/3 doped ceramics with 3 wt% H 3 BO 3 were designed as a patch antenna and a dielectric resonator antenna [221] . The solid solution of Li 2 Table 1 [224, , and the phase diagram of rock-salt structure is plotted in Fig. 8 , where the ordered-disordered range was summarized from Zhang et al. [246, 247] . Simultaneously, Gu et al. [248] stated the two-phase and thermally stable ceramics of 0.8Li 3 NbO 4 -0.2Ca 0 [250] , and a near zero τ f (-4.03 ppm/ ) was ℃ obtained for 0.1 mol Zn substitution for Mg [251] . [253] .

Except for the sintering temperature, the heating rates and substation will directly influence the grain size, densification, and properties. Lu et al. [254] pointed out that the sintering rate increasing from 3 to 7 /min would deteriorate the quality f ℃ actor of Li 2 ZnTi 3 O 8 ceramics. If ball milling is applied for the raw materials at first for 4 h, then the sintering temperature of Li 2 ZnTi 3 O 8 ceramics could reduce from 1075 to 925 , and those ceramics were chemically ℃ compatible with Ag [255] . Sintering the ceramics in a box type electric furnace and in a microwave furnace would obtain Li 2 ZnTi 3 O 8 ceramics with the grain size of 38 and 7 µm, respectively [256] . Mg, Co, and Zn substitution for Zn in Li 2 ZnTi 3 O 8 increased the quality factor because of the more compact microstructure [257] [258] [259] . Whereas, the secondary phases were recorded after the introduction of Sr 2+ or (Sr x Ca 1-x ) into Li 2 ZnTi 3 O 8 [260] [261] [262] . Phase evolution of (1-x)Li 2 ZnTi 3 O 8 -xTiO 2 system indicated that pure Li 2 ZnTi 3 O 8 with cubic structure was observed when x ≤ 0.2 (the lattice parameter is similar to MgFe 2 O 4 with space group of Fm3m (227)), solid solution was exited in the range of 0.2 ≤ x ≤ 0.4 with cubic structure (the lattice parameters is similar to Zn 2 Ti 3 O 8 with space group of P4332 (212)), and rutile TiO 2 phase appeared when x ≥ 0.6 [263] . The τ f value moves from -15 to 102.4 in (1-x)Li 2 ZnTi 3 O 8 -xTiO 2 (0 ≤ x ≤ 0.4) [264] ; meanwhile, near zero τ f value was also achieved by Bari et al. [265] in this system. 4 wt% TiO 2 was added into Li 2 ZnTi 3 O 8 with different particle sizes, where the nanoparticles and micron particles all generated a more uniform microstructure and relative density reached to 98.5% [266] . Similar to TiO 2 -doped Li 2 ZnTi 3 O 8 ceramics, phase composition and properties of Li 2 Mg(Ti 1-x Sn x ) 3 O 8 (x = 0.1-0.25) were concluded as with 0.10 ≤ x ≤ 0.15, the spinel and rutile were co-exited; with 0.20 ≤ x ≤ 0.25, the spinel, rutile, and ilmenite were obtained [267] , and the optimal properties of Li 2 ZnTi 3 O 8 -0.2SnO 2 composite ceramics exhibited: ε r ≈ 20.9, Q×f value ≈ 89,500 GHz, and τ f ≈ -24 ppm/ [268] . The ℃ variation of dielectric properties with density of (1-x)Li 2 (Mg 0.95 Zn 0.05 ) 3 Ti 3 O 8 -xLi 2 TiO 3 (x = 0.727, 0.778, 0.821, and 0.889) was discussed systematically by Zhang et al. [269] . The concentration of oxygen vacancy, relative density, and decrease in damping behavior would influence the Q×f value of Li 2 ZnTi 3 O 8 -x wt% Nb 2 O 5 [270] . To trace the dielectric response of lattice vibration, the response process of dielectric loss in Li 2 ZnTi 3-x M x O 8 (M = Al 3+ , Nb 5+ , (Al 0.5 Nb 0.5 ) 4+ , www.springer.com/journal/40145 (Zn 1/3 Nb 2/3 ) 4+ , and (Li 1/4 Nb 3/4 ) 4+ ) was discussed systematically containing the conduction loss and lattice vibration loss [271] . The conduction loss which acts at frequency lower than terahertz is neglectful by researchers concentrating on MWDCs, while AC impedance analysis was used to identify the effect of dopants and the mechanism of conduction loss in this system. Combining the fitting THz time domain spectrum and far infrared reflectivity spectrum, the dielectric response was illustrated in depth based on lattice loss and conduction loss.

Ultra-low loss microwave dielectric materials of Li 2 Mg 3 TiO 6 -based ceramics are extensively studied via doping cations into Mg and Ti site. Bivalent cations [272] [275] [276] [277] proposed a reliable method which provided the Li-rich sintering atmosphere, and they obtained serial MWDCs based on Li-Mg-Sn/Ti oxides with excellent properties. The schematic representation of the devices provided with the Li-rich atmosphere is shown in Fig. 9 , and this similar method was gradually popularized to other systems with volatilization element to obtain the ceramics with dense microstructure. The negative τ f values can be compensated by Ca 0.8 Sr 0.2 TiO 3 , and the sample with 0.91Li 2 Mg 3 TiO 6 -0.09Ca 0.8 Sr 0.2 TiO 3 showed a τ f value of -3.65 ppm/ [278] . ℃ The phase evolution of Li 2 O-3MgO-mTiO 2 (1 ≤ m ≤ 6) was summarized as the phase diagram shown in Fig. 10 [298] or non-stoichiometric Li 3 Mg 2+x SbO 6 [299] have been probed and analyzed to explain the variation of dielectric properties through current theory including P-V-L theory, packing fraction, and C-M equations. It was interesting that the "dark hole" phenomenon of Li 2 TiO 3 was cured by adding Li 3 Mg 2 NbO 6 and the τ f value of 0.96Li 2 TiO 3 -0.04 Li 3 Mg 2 NbO 6 was 2.6 ppm/ [300] . Since yet there ℃ was no literature about the structure transformation of Li 2 TiO 3 -Li 3 NbO 4 -MgO to renew the understanding of rock-salt ceramics, Zhang et al. [247, 301, 302] gradually updated the reports about Li 3 Mg 2 NbO 6 -based ceramics. The phase transitions among the orthorhombic, cubic, and monoclinic were verified by XRD (Fig. 12) and TEM analysis (Fig. 13) . The systematical analysis of lattice evolution and ordering transformation indicated that the low dielectric loss of this system was mainly ascribed to the superlattice. The THz time-domain spectroscopy was firstly used in this system to evaluate the intrinsic dielectric loss associated with phonon oscillation. Meanwhile, the configurational entropy was calculated to explain the change of disordered and ordered crystal structures, where the disordering cubic phase generated much larger configurational entropy than the ordered orthorhombic and monoclinic phase (Fig. 14) . 

Since 1970, the exploration of BaO-TiO 2 system has been continuous renewed. Among them, BaO-4TiO 2 and 2BaO-9TiO 2 are the most extensively investigated ceramics as the representative ceramics with medium dielectric constant. The pseudo phase diagram of tungsten bronze structure and binary system based on BaO-TiO 2 system is shown in Fig. 15 . In contrast to other sections in this review, the investigations about the compounds within this phase diagrams are relatively less, because the study of ceramics in BaO-R 2 O 3 -TiO 2 (R = La-Gd) has been almost accomplished and widely used in the industry.

The frequency dependence of Q×f value was observed for Ba 2 Ti 9 O 20 ceramics, which was ascribed to the extrinsic dielectric loss [304] . [307] , which showed ε r ≈ 11-51, Q×f value ≈ 2400-88,000 GHz, and τ f ≈ (-73)-232 ppm/℃. Based on sol-gel method, Mg 5 Nb 4 O 15 nano-powders were obtained at 600 , ℃ and then the sintering temperature can be reduced to 1300 [204] . On the basis of P ℃ -V-L chemical bond theory, the relationship of chemical bond characteristic and microwave dielectric properties of Eu 2 TiO 5 was discussed deeply [308] . Meanwhile, the electron localization function (ELF) based on the first-principles calculation was evaluated to provide the information of bond covalency [309] , which provided a strategy to estimate the chemical bond characterization.

The different compositions of tungstenbronze-type with Ba 6-3x R 8+2x Ti 18 O 54 solid solution reported by Ohsato [310] in 2001, and the compounds were presented in Fig. 16 . The relative permittivity of BaO-R 2 O 3 -TiO 2 (R = La-Gd) was higher than 80, and the solid solubility region became narrower as the ionic radius of rare earth increasing [311] . The doping effect and the determination of crystal structure of Ba 6-3x R 8+2x Ti 18 O 54 were summarized in the review of dielectric materials for wireless communication [1] . After 2010, there are only a few studies focused on this system. Three distinct phases were formed using variable size TiO 2 reagents into BaO-Nd 2 O 3 -TiO 2 [312] . Ba 6-3x R 8+2x Ti 18 O 54 (BRT, R = La, Pr, Nd, Sm) solid solution family was reported with high permittivity. When x = 2/3, Ba 4 Nd 9.33 Ti 18 O 54 was regarded as the most investigated ceramics to lower its τ f value and sintering temperature or improve its Q×f value. Yao et al. [313] and Chen et al. [314] proposed that with Al 2 O 3 added BaO-Nd 2 O 3 -TiO 3 ceramics, the Q×f value would increase obviously. The temperaturestable ceramics could be obtained by Pb and Sr substitution for Ba 3 [325] , and Ba 4 (Pr 1-x Sm x ) 28/3 Al 4y/3 O 54 [326] . Among those reports, the analysis of Raman spectrum of Ba 3.75 Nd 9.5 Ti 18-z (Al 1/2 Nb 1/2 )O 54 enriched the theoretical study of tungstenbronze-type.

Ceramics based on the BaO-ZnO- TiO 

The ideal perovskite (written as ABO 3 ) is cubically symmetric with a space group of Pm3m, and the represented material is SrTiO 3 . Due to the flexibility of ABO 3 perovskite, variants of perovskite have been investigated, and the classification of perovskiterelated structure with representative structure is summarized in Fig. 17 . The perovskite-related structure contained cubic-type, orthorhombic-type, and hexagonaltype structures. For hexagonal-type structure, the twinned hexagonal structure means the closely packed AO 3 layers were stacked in the order of (ccch) 2 , while the shifted hexagonal structure corresponds to ccchhccc order. The typical representative of twinned structure is Ba 8 CoTa 6 O 24 and the shifted structure is Ba 8 CoNb 6 O 24 with eight-layer hexagonal perovskite structure [332] . The pseudo phase diagram of ABO 3 and complex ABO 3 type is provided in Fig. 18 . From cubic and orthorhombic to hexagonal perovskite structure, researchers have proposed that tolerance factor, distortion of octahedron, and temperature of phase transition determined the variation of τ f value, and the ordered/ disordered cations were primarily related to quality factor.

This section contains the ceramics with a general [397] , while a τ f value of 8.2 ppm/ was ℃ achieved for (Sr 0.2 Ga 0.488 Nd 0.208 )Ti 1-x Ga 4x/3 O 3 with x = 0.5 [398] . A dramatical decrease of τ f value from 1171 to -82 ppm/ was obtained for Sr(Zr ℃ x Ti 1-x )O 3 [399] . In the chemical formula of SrO(Sr 1-x Ba x TiO 3 ) n (x = 0, 0.5; n = 1-4), it is demonstrated that samples with n = 1, 2 had no dielectric non-linear behavior in the temperature range of (-165)-50 , while the ℃ tunability increased with n increasing [400] . Two second phases containing BaWO 4 and Ba 2 Ti 5 O 12 were observed in Ba 0.5 Sr 0.5 Ti1 -3y/2 W y O 3 system with y ≥ 0.02 [401] , and BaTiSiO 5 phase was indexed in Ba 0.4 Sr 0.6 Ti 1-y Si y O 3 [402] . The dielectric constant can be adjusted apparently in the Ba 0.4 Sr 0.6 TiO 3 -BaMoO 4 and Ba 0.5 Sr 0.5 TiO 3 -AMoO 4 (A = Ba, Sr) composite ceramics, where only cubic perovskite structure and scheelite structure were detected [403, 404] . However, the BaMoO 4 was observed when MgMoO 4 added into Ba 0.5 Sr 0.5 TiO 3 [405] . Adding Zr 0.8 Sn 0.2 TiO 4 into Ba 0.4 Sr 0.6 TiO 3 , the dielectric constant and dielectric loss increased with the increase of the content of Zr 0.8 Sn 0.2 TiO 4 [406] . Adding Fe power in Ba 0.4 Sr 0.6 TiO 3 ceramics indicated that the appearance of Fe 2+ and Fe 3+ would decrease the O vacancy concentrations and enhance the microwave dielectric properties [407] . In the ternary system of Ba 0.5 Sr 0.5 TiO 3 -MgO-Mg 2 TiO 4 [408] , Ba 0.5 Sr 0.5 TiO 3 -MgO-Mg 2 SiO 4 [409] , and (1-x-y)BaTiO 3 -xCr 2 [413] . Similar to CaTiO 3 , the effect of LnAlO 3 (Ln = Sm, Nd) on BaTiO 3 -based ceramics was systematically studied by Liu et al. [414] and Xie et al. [415] . Solid solution of Ba x Mg 1-x Ti 0.95 Sn 0.05 O 3 [416] and local 1:1 ordering in B-site of Sr(Ga 0.5 Nb 0.5 ) 1-x Ti x O 3 was verified by TEM and Raman spectroscopy, and the decline of quality factor stemmed from the anharmonicity by Ti substitution [417] . 0.2SrTiO 3 -0.8Ca 0.61 Nd 0.26 Ti 1-x Al 4x/3 O 3 ceramics also reached a near zero τ f value with x = 0.5 [418] .

(1-x)Mg(Ti 0.95 Sn 0.05 )O 3 -xBaTiO 3 compounds experienced a phase transition of tetragonal-structure BaTiO 3 , monoclinic-structure Ba 4 Ti 11 O 26 , and triclinic-structure Ba 2 Ti 9 O 20 [419] . Likewise, Sr (1-1.5x) Ce x TiO 3 (x = 0.1-0.67) ceramics changed from cubic, tetragonal, to orthorhombic, and the dielectric behaviors were dominated by oxygen vacancies and defect dipoles [420] . Tian et al. [421, 422] reported that (Co 0.5 W 0.5 ) 4+ and (Zn 0.5 W 0.5 ) 4+ occupying the Ti-site in BaTiO 3 would render the τ f value change from positive to negative. BaWO 4 phase appeared in Ba 1-x Sr x (Mg 0.5 W 0.5 )O 3 ceramics and Ba 2 Mg 0.95 Zn 0.05 WO 6 , and the grain size distributed in a narrow range around 0.8 µm [423, 424] . [425] . In the nonstoichiometric system of (Sr 0.4 Ce 0.4 ) 1-x Nd x Ti 0.8 Mg 0.2 O 3 , solid solution was obtained when x ≤ 0.2, while the satisfied properties were ε r ≈ 53, Q×f value ≈ 26,700 GHz, and τ f ≈ +2.8 ppm/ with ℃ x = 0.4 [426] . Meanwhile, compositional dependence of microwave dielectric properties of doped SrTiO 3 sintered in air is presented as Fig. 19 . It was demonstrated that SrTiO 3 added into ZnAl 2 O 4 -3Zn 2 SiO 4 -2SiO 2 could reduce the sintering temperature from 1320 to 1180-1200 ℃ [427] .

With the same general formula of ABO 3 , the investigations of NdGaO 3 , NdNbO 3 , and AgTa/NbO 3 are listed adjacently to CaTiO 3 and SrTiO 3 . Phase composition was identified for NdGaO 3 -Bi 0.5 Na 0.5 TiO 3 system, and new temperature-stable ceramics with 0.4NdGaO 3 -0.6Bi 0.5 Na 0.5 TiO 3 was obtained [428] . Order-disorder transformation of A-site-deficient perovskites plays a significant role in conductivity of materials. The investigation of crystal structure and dielectric properties of the Nd (1-x)/3 M x NbO 3 (M = Li, Ag; 0 ≤ x ≤ 0.2) suggested that the dielectric loss majored by the lithium or silver ionic conduction at low frequencies [429] . Solid solution of AgNb/TaO 3based ceramics was then studied extensively [430, 431] . Temperature-stable MWDCs with the formula of (La,Nd) 2/3 TiO 3 were studied by Saleem et al. [432] .

MgTiO 3 also belongs to the general formula of ABO 3 . The substitution for MgTiO 3 such as Ni, Zn, Co, and Mn for Mg has been investigated systematically [433] [434] [435] [436] , where (Mg 1-x Co x )TiO 3 ceramics were crystalized as ilmenite structure when x ≤ 0.5, and the secondary phase was detected with more doping cations [437] . (Zn 1-x Mg x )TiO 3 was prepared and demonstrated that the dielectric constant and loss decreased with Mg increase [438] . For Sn doped into Ti site in MgTiO 3 , in the range of x = 0.05-0.07, the ceramics exhibited excellent microwave dielectric properties of ε r ≈ 16.8-17.1, Q×f value ≈ 298,000-312,000 GHz, and τ f ≈ (-53)-(-50) ppm/ [439] . ℃ Mg 0.95 Co 0.05 TiO 3 ceramics possessed properties as ε r ≈ 17.03, Q×f value ≈ 170 THz, and τ f ≈ -40 ppm/ ℃ when prepared by Semi Alkoxide precursor method [440] . Gong et al. [441] obtained Mg(Sn 0.05 Ti 0.95 )O 3 ceramics with microwave dielectric properties ε r ≈17.6, Q×f value ≈ 328,543 GHz, and τ f ≈ -42 ppm/ , and ℃ Jia et al. [442] proposed that Mg(Ti 1-x Nb x )O 3 showed microwave dielectric properties: ε r ≈ 18.12, Q×f value ≈ 163,618 GHz, and τ f ≈ -40.1 ppm/ . Through sol ℃ -gel process, the quality factor of geikielite-type MgTiO 3 saturated when the ceramics sintered at 1200 [443] . ℃ After adding B 2 O 3 into MgTiO 3 , the composite ceramics could be densified at 1100 [444] . Investigation of ℃ introduction SrTiO 3 into Mg(Zr 0.05 Ti 0.95 )O 3 ceramics suggested that a close zero τ f value could achieve at 0.96Mg(Zr 0.05 Ti 0.95 )O 3 -0.04SrTiO 3 [445, 446] . In the study of a designed composition of MgTiO 3 (Mg/Ti = 1, 1.02, 1.04, 1.05, 1.07), the generation of MgTi 2 O 5 which derived from Mg/Ti = 1 was restrained, and then pure phase of MgTiO 3 was obtained when Mg/Ti = 1.02 [447] . (Co 1-x Zn x )TiO 3 sintered at 1350 possessed ℃ ε r ≈ 20, Q×f value ≈ 107,000GHz, and τ f ≈ -60 ppm/ ℃ with x = 0.05 [448] . The choice of raw material of MgO and Mg(OH) 2 had a major influence on the phase formation and dielectric loss for 0.97MgTiO 3 -0.03SrTiO 3 [449] . In the system of (1-x)MgTiO 3-x Mg 2.05 SiO 4.05 -0.06CaTiO 3 , τ f ≈ 1.45 ppm/ was obtained with ℃ x = 0.2 [450] . ZnTiO 3 -type phase, Zn 2 TiO 4 -type, and TiO 2 phase were co-existed in (Zn 0.3 Co 0.7 )Ti 1-x Sn x O 3 , and the satisfied microwave dielectric properties were ε r ≈ 24, Q×f value ≈ 66,700GHz, and τ f ≈ -5.43 ppm/ ℃ with x = 0.02 [451] . It was interesting that MgTiO 3 and Mg 2 TiO 4 were the main phases in Mg n+1 Ti n O 3n+1 (n = 2, 3, 4, 5, 6, and 7), and the Mg 2 TiO 4 was effectively inhibited with n increasing [452] . New cofired tri-layer ceramic architecture of MgTiO 3 /TiO 2 /MgTiO 3 was designed to realize the temperature-stable and ultrahigh-Q ceramics, where the property comparison of MgO-TiO 2 system (Fig. 20) [453] . Mg 2 TiO 4 -related and Mg 6 Ti 5 O 16 -based ceramics in MgO-TiO 2 system were also reported. Mg 6 Ti 5 O 16 -based MWDCs were systematically investigated by Yu et al. [454] , where the τ f value could be adjusted to -3 ppm/℃ by Ca 2+ substitution. To explore the application for mobile communication, Nb 5+ ion was added into Mg 2 SnO 4 to improve the quality factor [455] . By mechanical synthesis method, the value of quality factor was sensitive to the initial particle size and microstructure of Mg 2 TiO 4 [456] . Meanwhile, the oxygen vacancies and average sizes were highly influenced on the dielectric loss of adding La 2 O 3 , V 2 O 5 , and CeO 2 into Mg 2 TiO 4 [457, 458] . A maximum quality factor value of 210,700 GHz was obtained in (Mg 1-x Zn x ) 1.8 Ti 1.1 O 4 with x = 0.06 [459] .

[(Mg 0.5 Zn 0.5 ) 0.95 Co 0.05 ] 2 TiO 4 was demonstrated as the optimal composition in the solid solution of (Mg, Zn) 2 TiO 4 -Co 2 TiO 4 with Q×f value ≈ 2100,000 GHz [460] . The average particle size of pure Mg 2 TiO 4 nano-powders was reduced to 163 nm via high energy ball milling method, and the excellent properties were ε r ≈ 13.9, Q×f value ≈ 98,600 GHz, and τ f ≈ -50.9 ppm/ [461] . Similarly to the formula of Mg ℃ 2 TiO 4 , spinel-based CoZnTiO 4 ceramics were obtained after sintered at 1200 , and th ℃ e properties were majored by the relative density and grain size [462] . Solid solution of Mg 2 (Ti 1-x Sn x )O 4 [463] and ZnNiTiO 4 /ZnNiTi 1-x Sn x O 4 [464, 465] was also reported. Until now, the intrinsic dielectric behavior of Mg 2 TiO 4 based on P-V-L theory and infrared spectra was presented by Li et al. [466] , where the Ti(1)-O bond plays a primary role in dielectric loss. Meanwhile, Mg 2 Ti 1-x Ga 4x/3 O 4 would reach a Q×f value ≈ 205,416 GHz [467] . Furthermore, there are some compounds in the formula of Na 0.5 Ln 0.5 TiO 3 (Ln = Sm, Nd). Fang et al. [468] and Zhou et al. [469] reported a serials of substitution, such as Na 0.5 Nd 0.2 Sm 0.3 Ti 1-x Sn x O 3 , Na 0.5 Nd 0.5 Ti 1-x Sn x O 3 , Na 0.5 Nd 0.2 Sm 0.3 Ti 1-x Zr x O 3 [470] , and Na 1/2 Sm 1/2 Ti 1-x (Cr 1/2 Nb 1/2 ) x O 3 [471] . Near zero τ f value appeared in Li 0.5 Sm 0.5 TiO 3 -Na 0.5 Sm 0.5 TiO 3 [472] .

Due to the flexibility and adjustability of the crystal structure of perovskite, the investigation of complex perovskite with various cations occupying Ti site gradually emerged. The structural studies of A 2 B′B″O 6 (A = Ba, Sr, Ca; B′ = lanthanide, Mg, Cr, Bi; B″ = Nb, Ta, Sb, W) indicated that phase transitions were ascribed to the tilting of B′O 6 /B″O 6 . In the Ba 2-2x Sr 2x SmSbO 6 system, phase transitions of Fm3m, I 2 /m, and P2 1 /n were observed and the τ f value shifted from +25 to -50 ppm/ [473] . Effect of non ℃ stoichiometry Ba 1+x (MgW) 1/2 O 3 , Ba(Mg 1+y W) 1/2 O 3 , and Ba(MgW 1+z ) 1/2 O 3 and the sintering temperature on microwave dielectric properties was systematically investigated by Wu and Bian [474] and Chen et al. [475] , respectively. A zero τ f value ceramic was obtained in Ba 2 Mg 1-x Ca x WO 6 system with x = 0.1 [474] . First-principles calculation of assignment for vibrational spectra of Ba(Mg 1/2 W 1/2 )O 3 MWDCs is shown in Fig. 21 [476] , which proposed that F 1u (2) modes originated from Mg-O 6 vibrations had the largest contribution to the dielectric properties. The investigation of microwave dielectric properties of giant permittivity ceramics with a A 2 B′B″O 6 formula (Ba(Fe 1/2 Nb 1/2 )O 3 and Sr(Fe 1/2 Nb 1/2 )O 3 ) indicated that the permittivity was independent of frequency [477] .

Ln(B 0.5 C 0.5 )O 3 (Ln = La, Sm, Nd; B = Mg, Zn; C = Ti, Sn) ceramics belonging to the general formula of A 2 B′B″O 6 have been reported as low dielectric loss materials with an adjustable temperature coefficient of resonant frequency. Among them, minor amount of low-melt point oxide of Bi 2 O 3 and B 2 O 3 was usually used to enhance the sintering densification of Sm(Mg 0.5 Ti 0.5 )O 3 [478, 479] , CuO was added into La 2.98/3 Sr 0.01 (Mg 0.5 Sn 0.5 )O 3 to enhance the densification [480] , and V 2 O 5 was valid for reducing the sintering temperature of Nd(Zn 1/2 Ti 1/2 )O 3 [481] . Solid solution of Nd (1-x) Sm x (Mg 0.5 Sn 0.5 )O 3 [482] , Nd(Mg 0.5-x Co x Sn 0.5 )O 3 [483] , Nd ( [499, 500] , La(Mg 0.5-x Sr x Sn 0.5 )O 3 [501] , Ca 0.6 La 0.267 TiO 3 -Ca(Sm 0.5 Nb 0.5 )O 3 [502] , and La[Al 1-x (Mg 0.5 Ti 0.5 ) x ]O 3 [503] was investigated based on sintering behavior and microstructure. Not only the investigations reported the microwave dielectric properties, but also the structure-property relationship containing intrinsic loss, vibrational modes, and chemical bond characteristics of Y 2 MgTiO 6 was studied in detail, and the schematic representation of vibrational modes of Y site was presented in Fig. 22 [504] . [511] . Adding MnO 2 into Ba(Co 1/3 Nb 2/3 )O 3 would enhance the grain growth and restrain the evaporation of CoO [527] . Meanwhile, the influence of B″-site non-stoichiometry of Ba(Co 0.56 Y 0.04 Zn 0.35 ) 1/3 Nb 2/3+x on properties was reported by Tang et al. [528] , where Ba 5 Nb 4 O 15 as a secondary phase was recorded. Simulation is carried out for Ba(Zn 1/3 Ta 2/3 )O 3 for the design of linear metal taper [529] . Peng et al. [530] reported that addition of La 2 O 3 into Ba(Mg 1/3 Ta 2/3 )O 3 , Ba 1-x Ca x (Mg 1/3 Ta 2/3 )O 3 , and Ba[Mg 1-x Zn x ] 1/3 Ta 2/3 O 3 led to the appearance of Ba 0.5 TaO 3 , and τ f value reached to near zero [531, 532] . The optimal properties of Ba[Mg (1-x)/3 Sn x Ta 2(1-x)/3 ]O 3 exhibited as ε r ≈ 24.1, Q×f value ≈ 138,500 GHz, and τ f ≈ +0.2 ppm/ [533] .

℃ The variation of τ f values for 1:1 and 1:2 complex perovskites was clarified to be mainly relevant with tolerance factors, which are summarized in Fig. 24 [524] . It has been verified that samples with non-stoichiometric Mg 2+ and Ta 5+ in Ba(Mg 1/3 Ta 2/3 )O 3 exhibited a wide temperature stability [525, 534] , and the correlations between Q×f versus ε r and τ f versus ε r of high-Q (≥ 100,000 GHz) MWDCs are presented in Fig. 25 . 

Perovskite-related oxides of series A n B n O 3n+2 = ABO x (x = 3+2/n) (A = Ca, Sr, or La and B = Ti or Nb) with n = 4, 4.33, 4.5, 5, 6, and 7 have been a focus owing to their electronic and dielectric properties. The crystal type and the physical properties rely on the value of n, which descripts the number of octahedral layers in the slabs [535] . Besides Ca 5 TaO 11 is an member of n = 3 in this series, and the textured La 3 Ti 2 TaO 11 was fabricated by spark plasma sintering, showing that grain-orientation control was an effective way to tailor the properties of this ceramic [541] . SrCa 4 Nb 4 TiO 17 and Ca 5 Nb 4 TiO 17 sintered at their optimal temperature presented an elongated and plate-like grain [542] . From 0 to 4, the τ f value shifted from -117 to 415 in NaCa 4-x Sr x Nb 5 O 17 [543] , while the τ f value changed in the range of (-117)-473 ppm/ for ℃ Na 1-x K x Ca 4 Nb 5 O 17 [544] .

The dielectric properties of Ca 4 La 2 Ti 5 O 17 were firstly reported by Rejini et al. [545] , which were crystalized as perovskite structure and the XRD results were matched well based on the formula of Ca 0 [551, 552] through spectroscopic methods. In the microwave frequency region, the Q×f value and τ f values of Ba 8 (Mg 1-x Zn x )Ta 6 O 24 ceramics decreased with the augment of x [553] . Similarly, a single phase with hexagonal 8H perovskite structure of Ba 8 Ti 3 Nb 4-x Sb x O 24 ceramics was prepared, and τ f value declined from 110 to 2 ppm/ [554] . ℃ BaWO 4 was used to adjust the large τ f value of 8H hexagonal perovskite Ba 4 LiNb 3 O 12 , and the properties of ε r ≈ 16.9, Q×f value ≈ 75,500 GHz, and τ f ≈ +8.7 ppm/ were obtained [555] . Phase transformation in ℃ the sequence of hexagonal, hexagonal along with cubic, and cubic was observed in Ba 4 LiNb 3-x Sb x O 12 and Ba 4 LiTa 3-x Sb x O 12 system. Especially, the optimal microwave dielectric properties were achieved for Ba 4 LiNb 2 SbO 12 with a zero τ f [556, 557] . τ f value dropped from positive to negative in Ba 3 LiTa 3-x Sb x Ti 5 O 21 [558] , and Ba 3 LiNb 3-x Sb x Ti 5 O 21 [559] , while the τ f value just reduced from 205 to 70 ppm/ for Ba ℃ 3 LiNb 3-x Ta x Ti 5 O 21 [560] . A-site deficient perovskite structure was well matched for LiSmTa 4 O 12 ceramics with tetragonal perovskite structure (A-site deficient perovskite structure), and the optimal microwave dielectric properties were ε r ≈ 59.60, Q×f value ≈ 7760 GHz, and τ f ≈ +41.8 ppm/℃ [561] .

Researchers paid their attention to Ruddlesden-Popper (R-P) structure until the dielectric properties of CaReAlO 4 (Re = Nd, Sm, Y) were reported. The general formula of R-P compounds was written as (A,A′) n+1 B n O 3n+1 , where the structure was built by corner-sharing (BO 6 ) octahedral and interlayer of ((A,A′)O). MLnAlO 4 and SrLn 2 Al 2 O 7 (M = Ca, Sr; R = Y, Sm, Nd, La) belong to the R-P series with n = 1 and 2, respectively. The crystal structures of SrLaAlO 4 and SrLa 2 Al 2 O 7 are presented in Fig. 26 . Single crystals of ABCO 4 layered compounds with K 2 NiF 4 structure were used as substrates for high-temperature superconductive thin films, while dielectric properties in this system were mainly investigated by Chen and his co-workers [562] [563] [564] [565] [566] [567] [568] [569] [570] [571] [572] [573] [574] . They contributed to analyze the relation between the intrinsic dielectric properties and crystal structure of MRAlO 4 (M = Ca, Sr; and R = Y, Sm, Nd, La). Combining the compression/dilation effects of different cation-oxygen bonds and the stability of crystal structure with vibrational spectrum, they emphasized that the drop of the quality factor was ascribed to the abnormal variations of axial bonds and the theoretical dielectric loss was obtained after fitted the infrared reflectivity spectra. With (Zn 0.5 Ti 0.5 ) 3+ substituted for Al 3+ of SrLaAlO 4 , the best combination of microwave dielectric properties was ε r ≈ 23.5, Q×f value ≈ 102,000 GHz, and τ f ≈ -3.4 ppm/℃ [572] . In the SrLaAlO 4 -Sr 2 TiO 4 system, some diffraction peaks shifted toward higher angles along with the variation of x, while some of them shifted toward lower angles, as shown in Fig. 27 [569] . This phenomenon was explained by the opposite change of a-axis and c-axis, where the octahedron elongated in the ab plane with the shrinkage in the c direction. The tolerance factor (t) of perovskite layer was used to evaluate the stability of those compounds, and the relation of t and r(M 2+ )/r(Ln 3+ ) was plotted in Fig. 28 [573] . Sr 0.6 Ca 0.4 LaAlO 4 with 10 wt% TiO 2 presented a near zero τ f ≈ -2.5 ppm/ [575] . On the other hand, the R-P structure such as Sr n+1 Ti n O 3n+1 (n = 1, 2) [576] , SrLn 2 Al 2 O 7 (Ln = La, Nd, Sm) [577] [578] [579] [580] [581] , was also established as K 2 NiF 4 structure. The interlayer polarization was verified to influence the microstructure and internal stress, and the complete structure information of SrLn 2 Al 2 O 7 ceramics was obtained by TEM. Solid solution of (Sr 1-x Ca x ) 2 TiO 4 [582] , Sr 2 Ti 1-x Sn x O 4 [583] , Sr 2 [Ti 1-x (Al 0.5 Nb 0.5 ) x ]O 4 [584] , and (Sr 1-3x/2 La x ) 2 Ti 1-y Ce y O 4 [585] was prepared to reduce the large τ f value of Sr 2 TiO 4 . Moreover, Sr 2 CeO 4 was obtained by Dai and Zuo [586] , and the substitution of Ti 4+ for Ce 4+ in Sr 2 CeO 4 generated a ceramic with excellent properties of ε r ≈ 20.7, Q×f value ≈ 115,550 GHz, and τ f ≈ -1.8 ppm/ . ℃

Although the pseudo phase diagrams contain various primary systems, some ceramics such as CeO [591] . Vibrational spectroscopy and microwave dielectric properties of Ca 3 Ln 2 W 2 O 12 (Ln = La, Sm) were analyzed by Liu and Song [592] , and the ε r of those two phases were 18.7 and 19.5. Ln 2 MoO 6 (Ln = La, Y) ceramics possessed a relative permittivity of 14.1-17.1, and the quality factor was 67,090 GHz for La 2 MoO 6 and 27,760 GHz for Y 2 MoO 6 , respectively [593] .

In the wake of the update of computer science, date-driven approaches including data mining and machine learning have been applied in many disciplines for obtaining the obscure quantitative relationships. For material science, machine learning was used to realize the property prediction, composition optimization, and experimental design [594] [595] [596] [597] [598] [599] [600] . Qin et al. [601] employed five commonly-used algorithms with 32 intrinsic chemical, structural, and thermodynamic features for modeling to predict low permittivity materials, where a database of 3300 materials has not been reported and the distribution of permittivity in virtual space of materials was shown in Fig. 29 . Quantitative prediction of the Q×f value of gillespitetype ACuSi 4 O 10 (A = Ca, Sr, Ba) ceramics was obtained by machine learning, and the results of (Ca x Sr 1-x )CuSi 4 O 10 and (Ba y Sr 1-y )CuSi 4 O 10 ceramics matched well with the experimental Q×f value, as shown in Fig. 30 [602] .

MWDCs with a suitable permittivity, low dielectric loss, and temperature stability are a perpetual pursuit for researchers. Those ceramics offer technoeconomic advantages including integration, lightweight, and reliability. With the continuous exploration, significant progress is presently being made in designing new compounds, analyzing the polarization mechanism along with the origin of dielectric loss, and predicting the microwave dielectric properties by theoretical model of machine learning. The relevant computational and experimental methods currently used to probe, predict, and understand intrinsic mechanisms are covered in this review. Because target ceramic system and their associated investigations are so diverse, we provide a brief classification on the composition of ceramics using pseudo phase diagram. The exploration of substitution of the given ceramics or new compounds is listed briefly following the pseudo phase diagram. Experimentally, it appears that substitution and composite ceramics are the most common used methods to optimize the microwave dielectric properties for a given system (reduce dielectric loss or adjust the τ f value to near zero). The previous doping researches are concentrated on single ion substitution, while more development of the co-doping (group of two aliovalent cations with a certain mole ratio) appears recently. For the probe of new dielectric materials, the new system usually belongs to germanate and gallate, besides the familiar system of silicate, titanate, niobate, and tantalate. Comparing with conventional solid state reaction method, fabrication techniques containing solution-processed sol-gel method, high energy ball milling method, spark plasma sintering, and microwave sintering have been demonstrated as the promising approaches to improve the properties or sintering behaviors so far. Providing the atmosphere with the volatile element in the sintering procession is a valid method to reduce the pores. Multi-layer ceramic architecture has been verified as a design for temperature-stable ceramics, and the wide application for more system or in the industry is waiting for the exploration.

The influence factor of microwave dielectric properties evolves extrinsic and intrinsic parts. The defects such as porosity, microstructure, and secondary phase are related to the relative density and grain size, which are extrinsic factors. Those results of a unique ceramics can be easily obtained by XRD and SEM, while the investigation of dielectric responded mechanism of intrinsic part is difficult due to the restrain of characterization techniques and the lack of general theory. Theoretically, from Clausius-Mossotti equation, packing fraction, cation valence, distortion of octahedron to the combination of P-V-L theory, lattice dynamics, and THz time-domain spectroscopy with the first-principles calculation, the intrinsic mechanism for MWDCs is gradually created. Recent efforts to employ P-V-L theory and infrared reflectivity spectra to understanding the intrinsic mechanism seem to be an easy and potential approach to draw conclusions for prediction the microwave dielectric properties. However, the development of "try and error" situation in experiments is a long-term procession. Toward this state end, greater fundamental understanding of dielectric response mechanism and increased practical performance metrics are required. The experimental trials and theoretical calculation serve as a database of MWDCs, and then, the machine learning is applied to predict new materials and their microwave dielectric properties. There has been an emerging trend about machine learning to provide new insight to draw a general conclusion to verify the effect of each factor on the variation of microwave dielectric properties. Challenges remain in the reconciliation of conclusion between existing theoretical approaches, the evaluation of P-V-L theory on microwave dielectric properties, and the advancement of first-principles calculation for describing the state of bond. Based on the theoretical analysis of MWDCs and the careful control of extrinsic influence, more comprehensive applicationspecific analyses to justify their adoption in electronic market may be able to complete.

While there is always a need for fundamental research, the acceleration of the commercial application of new materials and property optimized ceramics is another persistent target for researchers. This includes ending the limitation of currently available system and exploration materials with stable and excellent properties for electronic market. For example, alternative materials with satisfied microwave dielectric properties equal to perovskite ceramics are required in the industry. With the development of 5G and 6G, there is an urgent need for ceramics with ultra-low dielectric constant (< 5), low dielectric loss, and excellent temperature-stability in high frequencies. The compounds of borate, aluminate, silicate, and fluoride with low polarization should take into consideration as promising candidate. It may be a direction for discovering composite materials consisted of ceramics and organics. Meanwhile, reducing the sintering temperature of ceramics for meeting the need of LTCC is a highly challenging issue owing to its advantages in fabrication of electronic devices. On the other hand, the repeatability of microwave dielectric properties and the normalized evaluation method should be emphasized. The advancement of preparation method with simplified procedures should be taken into consideration as well. The investigation combining the discussion of the performance of a simulated and fabricated device with the analysis of fundamental mechanism of structure-property relationship should be more popularized to provide an entire and systematical exploration. As a summary, the microwave dielectric properties listed in the references are presented in Figs. 31(a) and 31(b). Lastly, we hope this brief progress report helps to understand the recent experimental methods and suggests an insight to take a new research direction for MWDCs. 

Dielectric Materials for Wireless Communication

Forsterite ceramics for millimeterwave dielectrics

High-Q and temperaturestable microwave dielectrics in layer cofired Zn 1.01 Nb 2 O 6 / TiO 2 /Zn 1.01 Nb 2 O 6 ceramic architectures

MgTiO 3 /TiO 2 /MgTiO 3 : An ultrahigh-Q and temperature-stable microwave dielectric ceramic through cofired trilayer architecture

The mechanism of microwave response in layer-cofired Zn 3 Nb 2 O 8 -TiO 2 -Zn 3 Nb 2 O 8 ceramic architecture

Bond susceptibilities and ionicities in complex crystal structures

Low loss dielectric materials for LTCC applications: A review

Low temperature co-fired ceramics with ultra-low sintering temperature: A review

BiVO 4 based high k microwave dielectric materials: A review

Preparation and microwave dielectric properties of cristobalite ceramics

melilite-type BaCo 2 Si 2 O 7 ceramics

Synthesis, lattice energy and microwave dielectric properties of BaCu 2-x Co x Si 2 O 7 ceramics

Crystal structure, lattice energy and microwave dielectric properties of melilite-type Ba 1-x Sr x Cu 2 Si 2 O 7 solid solutions

Synthesis and microwave dielectric properties of Ca 3 SnSi 2 O 9 ceramics

Ca 3 MgSi 2 O 8 : Novel low-permittivity microwave dielectric ceramics for 5G application

Phase evolution, crystal structure, and microwave dielectric properties of gillespitetype ceramics

Effects of Ni 2+ substitution on the crystal structure, bond valence, and microwave dielectric properties of BaAl 2-2x Ni 2x Si 2 O 8-x ceramics

Structure and microwave dielectric properties of BaAl 2−2x Li 2x Si 2 O 8−2x ceramics

Rare earth silicates with the apatite structure

Crystal structure and microwave dielectric properties of LiRE 9

Microwave dielectric properties of SrRE 4 Si 3 O 13

Correlation between crystal structure and microwave dielectric properties of CaRE 4 Si 3 O 13 (RE = La, Nd, Sm, and Er)

Structure characterization and microwave dielectric properties of LiGa 5 O 8 ceramic with low-ε r and low loss

Structure, far-infrared reflectance spectra, and microwave dielectric properties of Ba 2 MGa 11 O 20

Effect of A-site cation on crystal structure and microwave dielectric properties of AGe 4 O 9 (A = Ba, Sr) ceramics

A 3 Y 2 Ge 3 O 12 (A = Ca, Mg): Two novel microwave dielectric ceramics with contrasting τ f and Q×f

Bond characteristics and microwave dielectric properties of (Li 0.5 Ga 0.5 ) 2+ doped Mg 2 Al 4 Si 5 O 18 ceramics

Microwave dielectric properties of silico-carnotite Ca 3 M 2 Si 3 O 12 (M=Yb,Y) ceramics synthesized via high energy ball milling

Raman spectra and microwave dielectric properties of novel garnet-type Ca 3 MZrGe 3 O 12

Raman spectra and properties of two low-ε microwave dielectric ceramics Ca 3 B 2 Ge 3 O 12 (B = Al, Ga)

Two novel garnet Sr 3 B 2 Ge 3 O 12 (B = Yb, Ho) microwave dielectric ceramics with low permittivity and high Q

The effects of TiO 2 addition on microwave dielectric properties of Y 3 MgAl 3 SiO 12 ceramic for 5G application

Structure and infrared reflectivity spectra of novel Mg 3 Ga 2 GeO 8 microwave dielectric ceramic with high Q

Crystal structure, Raman spectra and microwave dielectric properties of novel temperature-stable LiYbSiO 4 ceramics

Correlation between crystal structure and dielectric characteristics of Ti 4+ substituted CaSnSiO 5 ceramics

Crystal structure, phase compositions, and microwave dielectric properties of malayaite-type Ca 1−x Sr x SnSiO 5 ceramics

Improved microwave dielectric properties of novel low-permittivity Sn-doped Ca 2 HfSi 4 O 12 ceramics

Microwave dielectric loss of titanium oxide

Relationships between crystal structure and microwave dielectric properties of

Phase relations in the system titaniumdioxide-diniobium-zinc-hexoxide

Usage of P-V-L bond theory in studying the structural/property regulation of microwave dielectric ceramics: A review

A new temperature stable microwave dielectric material Mg 0.5 Zn 0.5 TiNb 2 O 8

Structure, microwave properties and low temperature sintering of Ta 2 O 5 and Co 2 O 3 codoped Zn 0.5 Ti 0.5 NbO 4 ceramics

Structure analysis and microwave dielectric properties of Ca x Zn 1−x Sn 0.08 Ti 1.92 Nb 2 O 10 ceramics

Structural evolution and microwave dielectric properties of xZn 0.5 Ti 0.5 NbO 4 -(1-x)Zn 0.15 Nb 0.3 Ti 0.55 O 2 ceramics

Effects of ZrO 2 substitution on crystal structure and microwave dielectric properties of Zn 0.15 Nb 0.3 (Ti 1−x Zr x ) 0.55 O 2 ceramics

Bond ionicity, lattice energy and structural evolution of Ta

Crystal structure refinement and microwave dielectric properties of new low dielectric loss AZrNb 2 O 8 (A: Mn, Zn, Mg and Co) ceramics

Characterization of microwave dielectric materials NiZrNb 2 O 8 based on the chemical bond theory

Preparation, characterization, and dielectric properties of wolframitestructure MnZrNb 2 O 8 ceramics at microwave frequency

New low-dielectricloss NiZrNb 2 O 8 ceramics for microwave application

Sintering characteristics and microwave dielectric properties of low loss ZnZrNb 2 O 8 ceramics achieved by reaction sintering process

Correlations of crystal structure, bond energy and microwave dielectric properties of AZrNb 2 O 8 (A = Zn, Co, Mg, Mn) ceramics

Preparation and microwave dielectric properties of low-loss MgZrNb 2 O 8 ceramics

Investigations of dielectric properties of wolframite A 0.5 Zr 0.5 NbO 4 ceramics by bond theory and far-infrared spectroscopy

Characterization of crystal structure and microwave dielectric properties of AZrNb 2 O 8 (A=Zn,Co, Mg,Mn) ceramics based on complex bond theory

Bond analysis of novel MnZrTa 2 O 8 microwave dielectric ceramics with monoclinic structure

Structure, phase composition, Raman spectra, and microwave dielectric properties of novel Co 0.5 Zr 0.5 TaO 4 ceramics

Extrinsic effects on microwave dielectric properties of high-Q MgZrTa 2 O 8 ceramics

A microwave dielectric material Mg 0.5 Zn 0.5 ZrNb 2 O 8

Microstructure and microwave dielectric characteristics of (Zn 1−x Co x )ZrNb 2 O 8 ceramics

Characterization of low loss microwave dielectric materials Zn 0.92 Co 0.08 ZrNb 2 O 8 based on the complex chemical bond theory

Crystal structure and microwave dielectric characteristics of Co-substituted Zn 1-x Co x ZrNb 2 O 8 (0 ≤ x ≤ 0.1) ceramics

Structural evolution, Raman spectra, and microwave dielectric properties of Zr-substituted ZnTiTa 2 O 8 ceramics

Crystal structure and microwave dielectric properties of the low dielectric loss ZnZr 1−x Sn x Nb 2 O 8 ceramics

A new microwave dielectric material ZnZr 0.8 Sn 0.2 Nb 2 O 8

Structure and microwave dielectric properties of MgZr(Nb 1−x Sb x ) 2 O 8 (0 ≤ x ≤ 0.1) ceramics

A novel low loss microwave dielectric ceramic ZnZrNb 1.84 Sb 0.16 O 8 with wolframite structure

A new microwave dielectric material ZnZrNbTaO 8

Dependence of microwave dielectric properties on the substitution of isovalent composite ion for Nb-site of MgZrNb 2−x (Sn 1/2 W 1/2 ) x O 8 (0 ≤ x ≤ 0.15) ceramics

Bond ionicity, lattice energy

bond energy and the microwave dielectric properties of non-stoichiometric MgZrNb 2+x O 8+2.5x ceramics

Relationship of the structural phase transition and microwave dielectric properties in MgZrNb 2 O 8 -TiO 2 ceramics

Crystal structure and microwave dielectric properties of novel (1−x)ZnZrNb 2 O 8 −xTiO 2 ceramics

Effect of H 3 BO 3 addition on the sintering behavior and microwave dielectric properties of wolframite-type MgZrNb 2 O 8 ceramics

Effects of B 2 O 3 addition on sintering behavior and microwave dielectric properties of ixiolite-structure ZnTiNb 2 O 8 ceramics

Effect of H 3 BO 3 on sintering behavior and microwave dielectric properties of monoclinal structure ZnZrNb 2 O 8 ceramics

A new microwave dielectric material Ni 0.5 Ti 0.5 NbO 4

Microwave dielectric properties of a new Cu 0.5 Ti 0.5 NbO 4 ceramics

Microwave dielectric properties of low loss microwave dielectric ceramics: A 0.5 Ti 0.5 NbO 4 (A = Zn, Co)

Microwave dielectric properties of sol-gel derived CoTiNb 2 O 8 ceramics

The microwave dielectric properties of (Ni,Zn) 0.5 Ti 0.5 NbO 4 solid solution

Microwave dielectric properties of temperature stable CoTiNb 2 O 8 -CoNb 2 O 6 composite ceramics

Temperature stable microwave dielectric ceramic CoTiNb 2 O 8 -Zn 1.01 Nb 2 O 6 with ultra-low dielectric loss

Crystal structure and microwave dielectric characteristics of Zr-substituted CoTiNb 2 O 8 ceramics

Ti 1−x Zr x ) 0.5 NbO 4 microwave dielectric ceramics based on structural refinement

Correlations between microwave dielectric properties and crystal structures of Sb-doped Co 0.5 Ti 0.5 NbO 4 ceramics

Magnetic ordering in CoTa 2 O 6 and NiTa 2 O 6

Crystal structure and magnetism in CoSb 2 O 6 and CoTa 2 O 6

Crystal chemistry, Raman spectra, and bond characteristics of trirutile-type Co 0.5 Ti 0.5 TaO 4 microwave dielectric ceramics

Synthesis of rutile-type solid solution Ni 1−x Co x Ti(Nb 1−y Ta y ) 2 O 8 (0 ≤ x ≤ 1, 0 ≤ y ≤ 1) and its optical property

Novel temperature stable NiSnTa 2 O 8 microwave dielectric ceramics with trirutile structure

Isothermal sections in the systems ZnO-AO 2 -Nb 2 O 5 (A=Ti,Zr,Sn) at 1473 K

Crystal structure and microwave dielectric properties of (Zn 1−x Co x )TiNb 2 O 8 ceramics

Microstructure and microwave dielectric characteristics of the Ca x Zn 1−x TiNb 2 O 8 temperature stable ceramics

Correlation of crystal structure and microwave dielectric properties for Zn(Ti 1−x Sn x )Nb 2 O 8 ceramics

Phase constitution, structure analysis and microwave dielectric properties of Zn 0.5 Ti 1−x Zr x NbO 4 ceramics

Correlation of crystal structure and microwave dielectric properties for ZnTi(Nb 1−x Ta x ) 2 O 8 ceramics

New low-loss microwave dielectric material ZnTiNbTaO 8

Crystal structure and microwave dielectric properties of ZnTi(Nb 1−x Ta x ) 2 O 8 ceramics

Structural dependence of microwave dielectric properties of ixiolite structured ZnTiNb 2 O 8 materials: Crystal structure refinement and Raman spectra study

Microwave dielectric properties of ZnO-Nb 2 O 5 -xTiO 2 ceramics prepared by reaction-sintering process

High-performance ZnTiNb 2 O 8 microwave dielectric www

ZnNb 2 O 6 -TiO 2 nano powders

Bond theory, terahertz spectra, and dielectric studies in donor-acceptor (Nb-Al) substituted ZnTiNb 2 O 8 system

Synthesis, characterization, and microwave dielectric properties of ternary-phase ixiolite-structure MgTiNb 2 O 8 ceramics

Dielectric properties of AB 2 O 6 compounds at microwave frequencies

Qualitative approach to the structural differences between some mixed metal oxides containing Sb 5+ , Nb 5+ and Ta 5+

Dielectric properties OF MNb 2 O 6 compounds (where M = Ca

Characterization and microwave dielectric properties of M 2+ Nb 2 O 6 ceramics

Effect of sintering temperature and time on microwave dielectric properties of CaNb 2 O 6 ceramics

Synthesis and microwave dielectric properties of columbite-structure MgNb 2 O 6 ceramics by aqueous sol-gel technique

Phase evolution, bond valence and microwave characterization of (Zn 1−x Ni x )Ta 2 O 6 ceramics

Relationship between bond ionicity, lattice energy, and microwave dielectric properties of Zn(Ta 1−x Nb x ) 2 O 6 ceramics

Enhanced microwave dielectric properties of ZnTa 2 O 6 ceramics with Sb 5+ ion substitution

Mg-substituted ZnNb 2 O 6 -TiO 2 composite ceramics for RF/microwaves ceramic capacitors

Microwave dielectric properties of (1−x)ZnTa 2 O 6 −xMgNb 2 O 6 ceramics

Tailoring of microwave dielectric properties in (1−x)ZnTa 2 O 6 −xNiNb 2 O 6 ceramics

Phase structure and microwave dielectric properties of Mn-doped

Phase structure and dielectric property of the ZnNb 2 O 6 −(Mg 0.3 Zn 0.7 )TiO 3 multiphase ceramics

Effects of V 2 O 5 addition on the microstructure and microwave dielectric properties of ZnNb 2 O 6 ceramics

Low-temperature synthesis and microwave dielectric properties of trirutile-structure MgTa 2 O 6 ceramics by aqueous sol-gel process

The dominance of paramagnetic loss in microwave dielectric ceramics at cryogenic temperatures

Crystal structure and microwave dielectric properties of (1−x)ZnTa 2 O 6 −xTiO 2 ceramics

Microstructural and microwave dielectric properties of ZnNb 2 O 6 ceramics prepared through microwave sintering

Intrinsic dielectric properties of columbite ZnNb 2 O 6 ceramics studied by P-V-L bond theory and Infrared spectroscopy

Preparation, characterization, and microwave properties of RETiNbO 6 (RE = Ce

Microwave dielectric properties of RETiTaO 6

Microwave dielectric properties and microstructures of RETiNbO 6 (RE = La, Sm and Y)

A novel self-composite property-tunable LaTiNbO 6 microwave dielectric ceramic

Sintering behavior, structural phase transition, and microwave dielectric properties of La 1-x Zn x TiNbO 6-x/2 ceramics

Phase structural transition and microwave dielectric properties in isovalently substituted La 1−x Ln x TiNbO 6 (Ln = Ce, Sm) ceramics

Octahedral distortion, phase structural stability, and microwave dielectric properties in equivalently substituted LaTiNbO 6 ceramics

Raman scattering and infrared reflectivity study of orthorhombic/monoclinic LaTiNbO 6 microwave dielectric ceramics by A/B-site substitution

Dielectric and optical properties of Ln 0.8 Lu 0.2 TiNbO 6 (Ln = Ce, Pr, Nd & Sm) ceramics

Microwave dielectric properties of rare-earth ortho-niobates with ferroelasticity

Effect of ion substitution for Nd 3+ based on structural characteristic on the microwave dielectric properties of NdNbO 4 ceramic system

Improved quality factor of NdNbO 4 microwave dielectric ceramic by Mn 2+ substitution

Effect of Zn 2+ substitution on sintering behavior and dielectric properties of NdNbO 4 ceramics

Study of the microwave dielectric properties of (La 1−x Sm x )NbO 4 (x = 0-0.10) ceramics via bond valence and packing fraction

Influence of Sm 3+ substitutions for Nd 3+ on the microwave dielectric properties of (Nd 1−x Sm x )NbO 4 (x = 0.02-0.15) ceramics

Complex chemical bond theory, Raman spectra and microwave dielectric properties of low loss ceramics NdNbO 4 -xAl 2 O 3

New temperature stable (Nd 1−x La x ) 1.02 Nb 0.988 O 4 microwave dielectric ceramics

The correlations among bond ionicity, lattice energy and microwave dielectric properties of (Nd 1-x La x )NbO 4 ceramics

Modification of NdNbO 4 microwave dielectric ceramic by Bi substitutions

Correlation of crystal structure and microwave dielectric properties of Nd 1.02 (Nb 1-x Ta x ) 0.988 O 4 ceramic

Enhanced microwave dielectric properties of NdNbO 4 ceramic by Ta 5+ substitution

The relationship between bond ionicity, lattice energy, coefficient of thermal expansion and microwave dielectric properties of Nd(Nb 1-x Sb x )O 4 ceramics

The correlations between electronic polarizability, packing fraction, bond energy and microwave dielectric properties of Nd(Nb 1−x Sb x )O 4 ceramics

Influence of (Al 1/3 W 2/3 ) 5+ co-substitution for Nb 5+ in NdNbO 4 and the impact on the crystal structure and microwave dielectric properties

Structure stability, bond characteristics and microwave dielectric properties of co-substituted NdNbO 4 ceramics

NdNb 1-x (Mg 1/4 W 3/4 ) x O 4 (0.02 ≤ x ≤ 0.06) solid solution characterized by infrared spectrum and complex chemical theory

Bond characteristics, vibrational spectrum and optimized microwave dielectric properties of chemically substituted NdNbO 4

Effect of CaTiO 3 addition on microwave dielectric properties of NdNbO 4 ceramics as multi-function material

Microwave dielectric properties of a new ceramic system NdNbO 4 with CaF 2 addition

Effects of MgO additive on microwave dielectric properties of NdNbO 4 ceramics

Crystal structure, infrared spectra, and microwave dielectric properties of the EuNbO 4 ceramic

Phase evolution, crystal structure, and microwave dielectric properties of water-insoluble (1-x)LaNbO 4-x LaVO 4 (0 ≤ x ≤ 0.9) ceramics

Optimization on quality factor of LaNbO 4 microwave dielectric ceramics

Packing fraction, bond valence and crystal structure of AVO 4 (A = Eu, Y) microwave dielectric ceramics with low permittivity

Anomalous dielectric behaviour during the monoclinic to tetragonal phase transition in La(Nb 0.9 V 0.1 )O 4

Optimization of sintering behavior and microwave dielectric properties of LaNbO 4 ceramics with NiO/CoO additive

Thermal expansion performance and intrinsic lattice thermal conductivity of ferroelastic RETaO 4 ceramics

The effect of ZrO 2 alloying on the microstructures and thermal properties of DyTaO 4 for high-temperature application

Investigation on microstructures and thermo-physical properties of ferroelastic (Y 1-x Dy x )TaO 4 ceramics

Effect of Al 3+ doping on mechanical and thermal properties of DyTaO 4 as promising thermal barrier coating application

First-principle calculations of crystal structures, electronic structures, and optical properties of RETaO 4

Structural, morphological and dielectric properties of ErNbO 4 prepared by the sol-gel method

Intrinsic dielectric loss in Zr 0.8 Sn 0.2 TiO 4 ceramics investigated by terahertz time domain spectroscopy

Single crystal structure refinement of a magnesium niobium oxide: Mg 4 Nb 2 O 9

Crystal structure of corundum type Mg 4 (Nb 2-x Ta x )O 9 microwave dielectric ceramics with low dielectric loss

Synthesis, characterization, and microwave dielectric properties of Mg 4 Nb 2 O 9 ceramics produced through the aqueous sol-gel process

Influence of sintering temperature on dielectric properties and crystal structure of corundum-structured Mg 4 Ta 2 O 9 ceramics at microwave frequencies

Synthesis and microwave dielectric properties of pseudobrookite-type structure Mg 5 Nb 4 O 15 ceramics by aqueous sol-gel technique

High frequency dielectric properties of A 5 B 4 O 15 microwave ceramics

Effect of MgO excess on structure and microwave dielectric properties of Mg 4 Nb 2 O 9 ceramics

Microwave dielectric properties of Mg 4 Nb 2 O 9 ceramics with excess Mg(OH) 2 produced by a reaction-sintering process

Dielectric properties and crystal structure of (Mg 0.95 Ni 0.05 ) 4 (Nb 1-x Ta x ) 2 O 9 ceramics

Microwave dielectric properties of Mg 4 Nb 2 O 9 -based ceramics with (B x W 1−x ) 5+ substitutions at Nb 5+ sites

Dielectric properties and mixture behavior of y(Mg 0.95 Co 0.05 ) 4 Ta 2 O 9 −(1−y)CaTiO 3 ceramic system at microwave frequency

Influence of sintering temperature on densification and microstructure of Zn 3 Nb 2 O 8 ceramics derived from nanopowders

Microstructure and dielectric properties of Zn 3 Nb 2 O 8 ceramics prepared by a two-stage sintering method

Microwave dielectric properties of Li 2+x Ti 1−4x Nb 3x O 3 (0 ≤ x ≤ 0.1)

Sintering behavior, microstructure and microwave dielectric properties of Li 2+x TiO 3 (0 ≤ x ≤ 0.2)

Enhanced sintering characteristics and microwave dielectric properties of Li 2 TiO 3 due to nano-size and nonstoichiometry effect

Phase equilibria in the system Li 2 O-TiO 2

Pseudobinary phase relations of Li 2 Ti 3 O 7

Microstructure and microwave dielectric properties of Li 2 Ti 1−x (Zn 1/3 Nb 2/3 ) x O 3 ceramics

Influence of (Mg 1/3 Nb 2/3 ) complex substitutions on crystal structures and microwave dielectric properties of Li 2 TiO 3 ceramics with extreme low loss

Effects of (Co 1/3 Nb 2/3 ) 4+ substitution on microstructure and microwave dielectric properties of Li 2 Ti 1-x (Co 1/3 Nb 2/3 ) x O 3 ceramics for applications in ceramic antenna

Design of a high-efficiency and -gain antenna using novel low-loss, temperature-stable Li 2 Ti 1-x (Cu 1/3 Nb 2/3 ) x O 3 microwave dielectric ceramics

New high Q microwave dielectric ceramics with rock salt structures: (1−x)Li 2 TiO 3 +xMgO system (0 ≤ x ≤ 0.5)

High-Q dielectrics using ZnO-modified Li 2 TiO 3 ceramics for microwave applications

Structural evolution and microwave dielectric properties of Li (3−3x) M 4x Nb (1−x) O 4 (M = Mg, Zn; 0 ≤ x ≤ 0.9

Microstructure and microwave dielectric properties of (1−y)Li 3 NbO 4 +yLi 2 TiO 3 (Li 2 SnO 3 ) ceramics

Low-loss microwave dielectrics using rock salt oxide Li 2 MgTiO 4

Microwave dielectric properties and its compatibility with silver electrode of Li 2 MgTi 3 O 8 ceramics

Microwave dielectric properties and low temperature sintering behavior of Li 2 CoTi 3 O 8 ceramic

Phase analysis and improvement of quality factor of Li 2 ZnTi 3 O 8 ceramics by annealing treatment

A new microwave dielectric material LiNi 0.5 Ti 0.5 O 2

ZnLi 2/3 Ti 4/3 O 4 : A new low loss spinel microwave dielectric ceramic

Preparation, phase structure and microwave dielectric properties of a new low cost MgLi 2/3 Ti 4/3 O 4 compound

Preparation, phase structure and microwave dielectric properties of CoLi 2/3 Ti 4/3 O 4 ceramic

Characterization and microwave dielectric properties of new low loss Li 2 MgZrO 4 ceramics

New high Q low-fired Li 2 Mg 3 TiO 6 microwave dielectric ceramics with rock salt structure

Enhanced sintering ability and microwave dielectric properties of LiZnNbO 4 ceramics with pretreatment of raw materials

Investigation of the microwave dielectric properties of Li 2 ZnTi 5 O 12 ceramics

New rock salt structure dielectric material Li 2 Ni 3 TiO 6 at microwave frequency

Crystal structure, infrared spectra and microwave dielectric properties of ultra low-loss Li 2 Mg 4 TiO 7 ceramics

Crystal structure, infrared spectra and microwave dielectric properties of new ultra low-loss Li 6 Mg 7 Ti 3 O 16 ceramics

A new Li-based ceramic of Li 4 MgSn 2 O 7 : Synthesis, phase evolution and microwave dielectric properties

A novel microwave dielectric ceramic Li 2 NiZrO 4 with rock salt structure

Characterization of low loss microwave dielectric materials Li 3 Mg 2 NbO 6 based on the chemical bond theory

A low ε r and temperature-stable Li 3 Mg 2 SbO 6 microwave dielectric ceramics

Crystal structure and microwave dielectric properties of a novel rock-salt type Li 3 MgNbO 5 ceramic

A new series of low-loss multicomponent oxide microwave dielectrics with a rock salt structure: Li 5 MgABO

Lattice evolution, ordering transformation and microwave dielectric properties of rock-salt Li 3+x Mg 2-2x Nb 1-x Ti 2x O 6 solidsolution system: A newly developed pseudo ternary phase diagram

Structural and microwave dielectric properties of the (1−x)Li 3 NbO 4 −xCa 0.8 Sr 0.2 TiO 3 thermally stable ceramics

Synthesis and microwave dielectric properties of Li 2 MgTiO 4 ceramics

Influence of ionic substitution on

Effects of Zn 2+ substitution on the crystal structure, Raman spectra, bond energy and microwave dielectric properties of Li 2 MgTiO 4 ceramics

Sintering characteristics, crystal structure, and microwave dielectric properties of Li 2 (Mg 0.9 A 0.1 ) 4 TiO 7 (A = Co 2+ , Ni 2+ , Mg 2+ , Zn 2+ , Ca 2+ )

Crystal structure and microwave dielectric properties of Li 4 Mg 3

Correlation of heating rates, crystal structures, and microwave dielectric properties of Li 2 ZnTi 3 O 8 ceramics

Processing of low-fired glass-free Li 2 MgTi 3 O 8 microwave dielectric ceramics

Effect of synthesis and sintering technique on the long-range 1:3 cation ordering and microwave dielectric loss of Li 2 ZnTi 3 O 8 ceramics

High Q microwave dielectric ceramics in the Li 2 (Zn 1−x A x )Ti 3 O 8 (A = Mg

02-0.1) system

Microwave dielectric properties of temperature stable Li 2 Zn x Co 1−x Ti 3 O 8 ceramics

Microwave dielectric characteristics of Li 2 (Mg 0.94 M 0.06 )Ti 3 O 8 (M = Zn, Co, and Mn) ceramics

Investigation on phase and microstructures of a temperature stable high-Q Li 2 Zn 0.95 Sr 0.05 Ti 3 O 8 microwave dielectric ceramic

Crystal structure, phase evolution and dielectric properties in the Li 2 ZnTi 3 O 8 -SrTiO 3 system as temperature stable high-Q material

Influence of Ca x Sr 1−x (0 ≤ x ≤ 1) substitution for Zn on microwave dielectric properties of Li 2 ZnTi 3 O 8 ceramic as temperature stable materials

Phase structure and microwave dielectric properties of (1−x)Li 2 Zn 3 Ti 4 O 12 − xTiO 2 ceramics

Phase evolution, microstructure, and microwave dielectric properties of reaction-sintered Li 2 ZnTi 3 O 8 ceramic obtained using nanosized TiO 2 reagent

Role of nano-and micron-sized particles of TiO 2 additive on microwave dielectric properties of Li 2 ZnTi 3 O 8 − 4 wt%TiO 2 ceramics

A high improved quality factor of Li 2 MgTi 3 O 8 microwave dielectric ceramics system

High-Q microwave dielectric materials of Li 2 ZnTi 3 O 8 ceramics with SnO 2 additive

Novel temperature stable Li 2 TiO 3 -based microwave dielectric ceramics with low loss

Crystal structure, Raman spectra, and microwave dielectric properties of high-Q Li 2 ZnTi 3 O 8 systems with Nb 2 O 5 addition

Oxygen vacancy regulation and its high frequency response mechanism in microwave ceramics

Microwave dielectric properties of low loss Li 2 (Mg 0.95 A 0.05 ) 3 TiO 6 (A = Ca 2+ , Ni 2+ , Zn 2+ , Mn 2+ ) ceramics system

Structure and microwave dielectric properties of Li 2 Mg 3 Ti 1-x (Al 1/2 Nb 1/2 ) x O 6 ceramics

Low-permittivity and high-Q value Li 2 Mg 3 Ti 1-x (Zn 1/3 Nb 2/3 ) x O 6 microwave dielectric ceramics for microstrip antenna applications in 5G millimeter wave

Phase evolution, structure and microwave dielectric properties of Li 2+x Mg 3 SnO 6 (x = 0.00-0.12) ceramics

Temperature stable and high-Q microwave dielectric ceramics in the Li 2 Mg 3−x Ca x TiO 6 system (x = 0.00-0.18)

Structure and microwave dielectric properties of the Li 2/3(1−x) Sn 1/3(1−x) Mg x O systems (x = 0-4/7)

A novel temperaturestable and low-loss microwave dielectric using Ca 0.8 Sr 0.2 TiO 3 -modified Li 2 Mg 3 TiO 6 ceramics

Sintering behavior, phase evolution and microwave dielectric properties of thermally stable Li 2 O-3MgO-mTiO 2 ceramics (1 ≤ m ≤

Characterization on low loss dielectric Li 2 MgTiO 4 ceramics based on chemical bond theory at microwave frequency

Li 4 Mg 3 Ti 2 O 9 : A novel low-loss microwave dielectric ceramic for LTCC applications

Relationships between crystal structure and microwave dielectric properties of Li 2 (Mg 1−x Co x ) 3 TiO 6 (0 ≤ x ≤ 0.4) ceramics

Novel series of ultra-low loss microwave dielectric ceramics: Li 2 Mg 3 BO 6 (B = Ti, Sn, Zr)

Phase composition, microstructure and microwave dielectric properties of rock salt structured Li 2 ZrO 3 -MgO ceramics

Effects of (Mg 1/3 Sb 2/3 ) 4+ substitutions on the sintering behaviors and microwave

Effect of zirconium deficiency on structure characteristics, morphology and microwave dielectric properties of Li 2 Mg 3 Zr 1−x O 6 ceramics

Synthesis, crystal structure and low loss of Li 3 Mg 2 NbO 6 ceramics by reaction sintering process

Effect of Co-substitution on microwave dielectric properties of Li 3 (Mg 1−x Co x ) 2 NbO 6 (0.00 ≤ x ≤ 0.10) ceramics

A novel temperature stable and high Q microwave dielectric ceramic in Li 3 (Mg 1−x Mn x ) 2 NbO 6 system

Crystal structure, densification, and microwave dielectric properties of Li 3 Mg 2 (Nb (1−x) Mo x )O 6+x/2 (0 ≤ x ≤ 0.08) ceramics

Crystal structure and enhanced microwave dielectric properties of Ta 5+ substituted Li 3 Mg 2 NbO 6 ceramics

Sintering behavior and microwave dielectric properties of V 5+ substituted Li 3 Mg 2 SbO 6 ceramics

Effect of Sb-site nonstoichiometry on the structure and microwave dielectric properties of Li 3 Mg 2 Sb 1−x O 6 ceramics

Effect of Zn 2+ substitution for Mg 2+ in Li 3 Mg 2 SbO 6 and the impact on the bond characteristics and microwave dielectric properties

Effects of W 6+ substitution on crystal structure and microwave dielectric properties of Li 3 Mg 2 NbO 6 ceramics

Crystal structure, bond energy, Raman spectra, and microwave dielectric properties of Ti-doped Li 3 Mg 2 NbO 6 ceramics

Crystal structures and high microwave dielectric properties in Li + /Ti 4+ ions co-doped Li 3 Mg 2 NbO 6 ceramics

Microwave dielectric properties of Li 3 Mg 2 NbO 6 -based ceramics with (M x W 1−x ) 5+ (M = Li + , Mg 2+ , Al 3+ , Ti 4+ ) substitutions at Nb 5+ sites

Crystal structure and enhanced microwave dielectric properties of nonstoichiometric Li 3 Mg 2+x NbO 6 ceramics

Low-loss and temperature-stable (1−x)Li 2 TiO 3 −xLi 3 Mg 2 NbO 6 microwave dielectric ceramics

Structural evolution and microwave

Effects of lattice evolution and ordering on the microwave dielectric properties of tin-modified Li 3 Mg 2 NbO 6 -based ceramics

Ultralow-loss and thermally stable Li 4 MgSn 2-1.25x Nb x O 7 microwave dielectric ceramics

Frequency-dependent Qf value of low-loss Ba 2 Ti 9 O 20 ceramics at microwave frequencies

Microwave dielectric properties of BaTi 4 O 9 -BaSm 2 Ti 4 O 12 composite ceramics

Improvement of microwave dielectric properties of Ba 2 Ti 9 O 20 ceramics using [Zn 1/3 Nb 2/3 ] 4+ substitution for Ti 4+

A 5 B 4 O 15

Structure, infrared spectra and microwave dielectric properties of the novel Eu 2 TiO 5 ceramics

First-principles investigation of structural, elastic and electronic properties of lanthanide titanate oxides Ln 2 TiO 5

Science of tungstenbronze-type like Ba 6-3x R 8+2x Ti 18 O 54 (R = rare earth) microwave dielectric solid solutions

The role of dopants in tailoring the microwave properties of Ba 6-x R 8+2/3x Ti

Phase analysis and microwave dielectric properties of BaO-Nd 2 O 3 -5TiO 2 composite ceramics using variable size TiO 2 reagents

Effects of Al 2 O 3 addition on the microstructure and microwave dielectric properties of Ba 4 Nd 9.33 Ti 18 O 54 ceramics

Dependence of microwave dielectric properties on site substitution in Ba 3.75 Nd 9.5 Ti 18 O 54 ceramic

Ba 1-y Pb y ) 3·75 Nd 9.5 Ti 18 O 54 and (Ba 1-y Sr y ) 3.75 Nd 9.5 Ti 18 O 54 microwave dielectric ceramics: Effect of Pb and Sr substitution on dielectric properties

Characterization of Ba 4 . 5 Re 9 Ti 18 O 54 (Re = La, Nd) microwave dielectric ceramics

Microstructure and microwave dielectric properties of Ba 4.2 Nd 9

Microwave dielectric properties and microstructure of (Ba 0.98 Sr 0.02 ) 3.75 Nd 9.5 Ti 18−x (Zn 1/3 Nb 2/3 ) x O 54 ceramics

Microwave dielectric properties and microstructure of

Microwave dielectric property modification of Ba 4 Nd 9.33 Ti 18 O 54 ceramics by the substitution of (Al 0.5 Nb 0.5 ) 4+ for Ti 4+ and the addition of NdAlO 3

Crystal structure, Raman spectroscopy and microwave dielectric properties of Ba 3.75 Nd 9.5 Ti 18−z (Al 1/2 Nb 1/2 ) z O 54 ceramics

Microstructure and microwave dielectric properties of Ba 6−3x Sm 8+2x Ti 18 O 54 ceramics with various Ba x Sr 1−x TiO 3 additions

Synthesis and microwave dielectric properties of BaO-Sm 2 O 3 -5TiO 2 ceramics with NdAlO 3 additions

Anti-reduction of Ti 4+ in Ba 4.2 Sm 9.2 Ti 18 O 54 ceramics by doping with MgO, Al 2 O 3 and MnO 2

Novel thermally stable, high quality factor Ba 4 (Pr 0.4 Sm 0.6 ) 28/3 Ti 18−y Ga 4y/3 O 54 microwave dielectric ceramics

A/B-site cosubstituted Ba 4 Pr 28/3 Ti 18 O 54 microwave dielectric ceramics with temperature stable and high Q in a wide range

Phase equilibria and crystal chemistry of the binary and ternary barium polytitanates and crystallography of the barium zinc polytitanates

The influence of Cu substitution on the microwave dielectric properties of BaZn 2 Ti 4 O 11 ceramics

Improved high-Q microwave dielectric ceramics in CuO-doped BaTi 4 O 9 − BaZn 2 Ti 4 O 11 system

Microwave dielectric properties of BaO−2(1−x)ZnO−xNd 2 O 3 −4TiO 2 (x = 0−1.0) ceramics

Ba 8 CoNb 6-x Ta x O 24 eight-layer shifted hexagonal perovskite ceramics with spontaneous Ta 5+ ordering and near-zero τ f

Sinterability and microwave dielectric properties of nano structured 0.95MgTiO 3 -0.05CaTiO 3 synthesised by top down and bottom up approaches

Structural, vibrational and microwave dielectric properties of

Microwave dielectric properties of (1−x)Mg 0.95 Zn 0.05 TiO 3 −(x)Ca 0.6 La 0.8/3 TiO 3 ceramic composites

Microwave and terahertz dielectric properties of MgTiO 3 -CaTiO 3 ceramics

A temperature-stable and high-Q

Microwave dielectric properties of (1−x)MgTiO 3 −x(Ca 0.6 Na 0.2 Sm 0.2 )TiO 3 ceramic system

Microwave dielectric properties of novel (1−x)MgTiO 3 −xCa 0.5 Sr 0.5 TiO 3 ceramics

Sintering behavior and microwave dielectric properties of (1−x)CaTiO 3 −xLaAlO 3 ceramics

Microwave dielectric properties and crystal structures of 0

Influence of LaAlO 3 additive to MgTiO 3 -CaTiO 3 ceramics on sintering behavior and microwave dielectric properties

LaAlO 3 doped (Mg 0.95 Zn 0.05 )TiO 3 -CaTiO 3 ceramic system with

ultra-high-Q and temperature-stable characterization

Investigation on microwave dielectric properties and microstructures of (1−x)LaAlO 3−x Ca 0.2 Sr 0.8 TiO 3 ceramics

Effect of Ga 3+ substitution on the microwave dielectric properties of 0.67CaTiO 3 -0.33LaAlO 3 ceramics

Sintering behaviors, microstructure, and microwave dielectric properties of CaTiO 3 -LaAlO 3 ceramics using CuO/B 2 O 3 additions

The sintering behavior and microwave dielectric properties of 0.67CaTiO 3 -0.33LaAlO 3 ceramics sintered at medium temperatures with the additives of H 3 BO 3 -Li 2 CO 3

Densification, microstructural evolution, and dielectric properties of CaTiO 3 -LaGaO 3 microwave ceramics

High-permittivity and low-loss microwave dielectric ceramics based on (x)RE(Zn 1/2 Ti 1/2 )O 3 −(1−x)CaTiO 3 (RE = La and Nd)

Composite dielectrics (1−y)(Mg 1−x Zn x ) 1.8 Ti 1.1 O 4 −yCaTiO 3 suitable for microwave applications

Effects of CaTiO 3 addition on the densification and microwave dielectric properties of BiSbO 4 ceramics

Influence of Ca 0.8 Sr 0.2 TiO 3 on the microstructures and microwave dielectric properties of Nd(Mg 0.4 Zn 0.1 Sn 0.5 )O 3 ceramics

Phase structures and microwave

AlO 3 ceramics

Microstructure and microwave dielectric properties of (1−x)Ca 0.6 La 0.267 TiO 3−x Ca(Mg 1/3 Nb 2/3 )O 3 ceramics

Effect of bond valence on microwave dielectric properties of (1−x)CaTiO 3−x (Li 0.5 La 0.5 )TiO 3 ceramics

High permittivity and near-zero τεdielectrics Ca 0.36 Sr 0.64 TiO 3 -Li 0.5 Nd 0.5 TiO 3 for multilayer ceramic capacitors

Correlation between vibrational modes of A-site ions and microwave dielectric properties in (1−x)CaTiO 3 −x(Li 0.5 Sm 0.5 )TiO 3 ceramics

Synthesis and characterization of CaTiO 3 -(Sm,Nd)AlO 3 microwave ceramics via sol−gel method

Effect of NdAlO 3 on microstructure, dielectric properties and temperaturestable mechanism of (Sr,Ca,Nd)TiO 3 ceramics at microwave frequency

Sintering behaviour and microwave dielectric properties of a new complex perovskite: (1−x)(Sr 0.3 Ca 0.427 Nd 0.182 )TiO 3 −xSmAlO 3 ceramics

Synthesis of 0.65CaTiO 3 -0.35SmAlO 3 ceramics and effects of La 2 O 3 /SrO doping on their microwave dielectric properties

Structure and microwave dielectric properties of CaSmAlO 4 -CaTiO 3 -Sm 0.9 Nd 0.1 AlO 3 ceramics with medium to high permittivity

Crystal structure, Raman spectra analysis and microwave dielectric properties optimization of (Ca 0.22 Li 0.39 Sm 0.39 )TiO 3 ceramics doped with SmAlO 3

Sintering behavior, phase structure and microwave dielectric properties of CeO 2 added CaTiO 3 -SmAlO 3 ceramics prepared by reaction sintering method

Tuning the microwave dielectric properties of Zn 2 SnO 4 ceramics by adding Ca 0.8 Sr 0.2 TiO 3

Crystal structure and dielectric properties of xCa

−x)(Ca 0.61 Nd 0.26 )TiO 3 at the microwave frequency

Effect of MgO on microstructure and microwave dielectric properties of 0

Microwave dielectric properties of (1−x)CaTiO 3 -x(Na 0.5 Nd 0.5 )TiO 3 ceramics

Structure and characterization of B 2 O 3 modified yNd(Mg 1/2 Ti 1/2 )O 3 -(1-y)Ca 0 .8Sr 0.2 TiO 3 ceramics with a near-zero temperature coefficient at microwave frequency

Microwave sintering and microwave dielectric properties of

Electrical microstructures of CaTiO 3 -Bi 0.5 Na 0.5 TiO 3 microwave ceramics with high www

r max ∼487)

Structure and dielectric properties of novel series of 3CaO-RE 2 O 3 -2WO 3 (RE = La, Nd and Sm) microwave ceramics and the adjustment of τ f value

Low-loss (1-x)Ba 0.6 Sr 0.4 La 4 Ti 4 O 15 -xCaTiO 3 microwave dielectric ceramics with medium permittivity

Preparation, structure and microwave dielectric properties of novel La 2 MgGeO 6 ceramics with hexagonal structure and adjustment of its τ f value

Microwave dielectric properties of (Ca 0.8 Sr 0.2 )(Sn x Ti 1−x )O 3 ceramics

Structure and microwave dielectric properties of Ca 0.7 Ti 0.7 La 0.3 (Al 0.3−x Ga x )O 3 ceramics

Structures and microwave dielectric properties of Ca (1−x) Nd 2x/3 TiO 3 ceramics

Microwave sintering of Ca 0.6 La 0.2667 TiO 3 microwave dielectric ceramics

Phase, microstructure and microwave dielectric properties of Nb and Ga doped Ca 0.6 La 0.267 TiO 3 ceramics

Structure and microwave dielectric characteristics of lithium-excess Ca 0

Microwave dielectric properties of Ca 0.4-x Mg x Sm 0.4 TiO 3 ceramics

Microwave dielectric properties of CaTi 1−x (Nb 0.5 Ga 0.5 ) x O 3 ceramics

Sintering behavior, microstructure, and microwave dielectric properties of Ca 0.66 Ti 0.66 Sm 0.34 Al 0.34 O 3 ceramics

Sintering behavior, microwave dielectric properties of Ca 0.66 Ti 0.66 Nd 0.34 Al 0.34 O 3 ceramics revealed by microstructure and Raman scattering

Structural and microwave ceramics

Structure evolution and improved microwave dielectric characteristics in CaTi 1−x (Al 0.5 Nb 0.5 ) x O 3 ceramics

Preparation and microwave dielectric properties of Ca 0.6 La 0.8/3 (Sn x Ti 1−x )O 3 ceramics

Investigation on structure and microwave dielectric properties of novel high dielectric constant Ca 1−3x/2 Ce x TiO 3 ceramics sintered in nitrogen atmosphere

Microwave dielectric characteristics

Characterization of structure, chemical bond and microwave dielectric properties in Ca 0.61 Nd 0.26 TiO 3 ceramic substituted by chromium for titanium

Effects of Magnesiumtungsten co-substitution on crystal structure and microwave dielectric properties of CaTi 1−x (Mg 1/2 W 1/2 ) x O 3 ceramics

Structural investigation and improvement of microwave dielectric properties in Ca(Hf x Ti 1−x )O 3 ceramics

Influence of thermal treatments on the low frequency conductivity and microwave dielectric loss of CaTiO 3 ceramics

Microwave dielectric properties of new (Ca 0.8 Sr 0.2 )SnO 3 ceramics

Microwave dielectric properties of (1−y)Nd 1−2x/3 Ba x (Mg 0.5 Sn 0.5 )O 3 −yCa 0.8 Sr 0.2 TiO 3 ceramic

Lattice vibrational characteristics and dielectric properties of pure phase CaTiO 3 ceramic

Microwave dielectric properties of Ba

Effects of structural characteristics on microwave dielectric properties of (Sr 0.2 Ca 0.488 Nd 0.208 )Ti 1−x Ga 4x/3 O 3 ceramics

Structural, microwave dielectric properties and dielectric resonator antenna studies of Sr(Zr x Ti 1−x )O 3 ceramics

Microstructure and dielectric tunable properties of SrO(Sr 1−x Ba x TiO 3 )n microwave ceramics

Microwave dielectric properties of low loss and highly tunable Ba 0.5 Sr 0.5 Ti 1−3y/2 W y O 3 ceramics

Structural and dielectric tunable properties of Ba 0.4 Sr 0.6 Ti 1−y Si y O 3 microwave ceramics

Property optimization of Ba 0.4 Sr 0.6 TiO 3 -BaMoO 4 composite ceramics for tunable microwave applications

Microwave dielectric properties of tunable Ba 0.5 Sr 0.5 TiO 3 and scheelite AMoO 4 (A = Ba, Sr) composite ceramics

Dielectric tunable properties of Ba 0.5 Sr 0.5 TiO 3 -MgMoO 4 composite ceramics for microwave applications

Enhanced microwave dielectric properties of Ba

Enhanced microwave dielectric properties of Ba 0.4 Sr 0.6 TiO 3 ceramics doping by metal Fe powders

Microstructures and dielectric tunable properties of Ba 0.5 Sr 0.5 TiO 3 -MgO-Mg 2 TiO 4 composite ceramics

Anomalous correlation between dielectric constant and tunability in (Ba,Sr)TiO 3 -MgO-Mg 2 SiO 4 composite ceramics

Effects of Bi 2 O 3 and Cr 2 Ti 3 O 9 co-doping on dielectric properties in BaTiO 3 -based ceramics

Microstructure and dielectric properties of highly tunable Ba 0.6 Sr 0.4 TiO 3 /MgO/Al 2 O 3 / ZnO composite

Manganese doping effects on interband electronic transitions, lattice vibrations, and dielectric functions of perovskite-type Ba 0.4 Sr 0.6 TiO 3 ferroelectric ceramics

Microwave dielectric properties of

Microstructures and microwave dielectric properties of (1−x)(Sr 0.4 Na 0.3 La 0.3 )TiO 3 −xLnAlO 3 (Ln = Sm, Nd) ceramic systems

Effect of ZnO/WO 3 additives on sintering behavior and microwave dielectric properties of (Sr,Ca)TiO 3 -(Sm,Nd)AlO 3 ceramics

Structural and dielectric properties of (Ba x Mg 1−x )(Ti 0.95 Sn 0.05 )O 3 (x = 0.025, 0.05, 0.075 and 0.1) solid solutions

Sr(Ga 0.5 Nb 0.5 ) 1−x Ti x O 3 low-loss microwave dielectric ceramics with medium dielectric constant

Microwave dielectric properties of 0.2SrTiO 3 -0.8Ca 0.61 Nd 0.26 Ti 1−x Al 4x/3 O 3 ceramics

Synthesis and characterization of temperature stable low-loss (1−x)Mg(Ti 0.95 Sn 0.05 )O 3 -(x)BaTiO 3 (0 ≤ x ≤ 0.1) ceramics for microwave applications

Structure and microwave dielectric behavior of A-site-doped Sr (1−1.5x) Ce x TiO 3 ceramics system

Structures and microwave dielectric properties of Ba

Crystal structures and microwave dielectric properties of Zn, W co-substituted BaTiO 3 perovskite ceramics

Microwave dielectric properties of (Ba 1-x Sr x )(Mg 0.5 W 0.5 )O 3 ceramics

Dielectric properties of Ba 2 Mg 0.95 Zn 0.05 WO 6 ceramics at microwave frequency

Structure and microwave dielectric properties of B-site deficient double perovskite-Ba[(Mg (1-x)Int

Phase evolution and microwave dielectric properties of SrTiO 3 added ZnAl 2 O 4 -Zn 2 SiO 4 -SiO 2 ceramics

Study on phase structures and compositions, microstructures, and

Structure and dielectric properties of A-site-deficient perovskite Nd 1−x/3 M x NbO

≤ x ≤ 0.20) ceramics

The microstructure and properties of Ag(Nb 0.8 Ta 0.2 ) 1−x (Mn 0.5 W 0.5 ) x O 3 ceramic system

Correlation between crystal structure and properties of ultra-high dielectric constant ceramics xSrCO 3 -Bi 2 O 3 -Ag(Nb,Ta)O 3

Phase, microstructure and microwave dielectric properties of A-site deficient (La,Nd) 2/3 TiO 3 perovskite ceramics

Structure and properties analysis for MgTiO 3 and (Mg 0.97 M 0.03 )TiO 3 (M = Ni, Zn, Co and Mn) microwave dielectric materials

Microwave and broadband dielectric properties of Ni substituted MgTiO 3 ceramics

Characterization of Zn doped MgTiO 3 ceramics: An approach for RF capacitor applications

Low dielectric loss characteristics of [(Mg 1−x Zn x )

Structure and properties analysis for low-loss (Mg 1−x Co x )TiO 3 microwave dielectric materials prepared by reaction-sintering method

Microwave dielectric properties of (Zn 1-x Mg x )TiO 3 (ZMT) ceramics for dielectric resonator antenna application

Correlation between Sn substitution for Ti and microwave dielectric properties of magnesium titanate ceramics

Effect of cobalt doping on the structural, microstructure and microwave dielectric properties of MgTiO 3 ceramics prepared by semi alkoxide precursor method

Microwave dielectric properties of high-Q Mg(Sn x Ti 1−x )O 3 ceramics

Structural dependence of microwave dielectric properties in ilmenite-type Mg(Ti 1-x Nb)O 3 solid solutions by Rietveld refinement and Raman spectra

Improvements in the sintering behavior and microwave dielectric properties of geikielite-type MgTiO 3 ceramics

Sintering behavior and microwave dielectric properties of MgTiO 3 ceramics doped with B 2 O 3 by sol-gel method

Influence of SrTiO 3 modification on dielectric properties of Mg(Zr 0.05 Ti 0.95 )O 3 ceramics at microwave frequency

Microwave dielectric properties of Mg(Zr 0.05 Ti 0.95 )O 3 -SrTiO 3 ceramics

Phase composition and microwave dielectric properties of Mg-excess MgTiO 3 ceramics

Low-loss microwave dielectric ceramics in the (Co 1−x Zn x )TiO 3 (x = 0-0.1) system

Effects of MgO and Mg(OH) 2 on phase formation and properties of strontium-doped MgTiO 3 microwave dielectric ceramics

Effects of Mg 2.05 SiO 4.05 addition on phase structure and microwave properties of MgTiO 3 -CaTiO 3 ceramic system

Structure and microwave dielectric properties of (Zn 0.3 Co 0.7 )Ti 1−x Sn x O 3 ceramics

Microstructures and microwave dielectric properties of Mg n+1 TinO 3n+1 ceramics with ultralow dielectric loss

Effects of adding B 2 O 3 on microwave dielectric properties of 0.9625MgTiO 3 -0.0375(Ca 0.5 Sr 0.5 )TiO 3 composite ceramics

Ultra-high quality factor of Mg 6 Ti 5 O 16 -based microwave dielectric ceramics with temperature stability

Microwave dielectric properties of Mg 1/3 Nb 2/3 SnO 4 ceramics

Structural and microwave dielectric properties of Mg 2 TiO 4 ceramics synthesized by mechanical method

Liquid phase effect of La 2 O 3 and V 2 O 5 on microwave dielectric properties of Mg 2 TiO 4 ceramics

Enhanced densification and microwave dielectric properties of Mg 2 TiO 4 ceramics added with CeO 2 nanoparticles

Dielectric properties of high-Q (Mg 1-x Zn x ) 1.8 Ti 1.1 O 4 ceramics at microwave

Dielectric properties and crystal structure of Mg 2 TiO 4 ceramics substituting Mg 2+ with Zn 2+ and Co 2+

Microwave dielectric properties of Mg 2 TiO 4 ceramics synthesized via high energy ball milling method

A novel low-loss spinel microwave dielectric ceramic CoZnTiO 4

Relationships between Sn substitution for Ti and microwave dielectric properties of Mg 2 (Ti 1−x Sn x )O 4 ceramics system

Enhancement quality factor of ZnNiTiO 4 microwave ceramics by substituting Ti 4+ with Sn 4+

Elucidating the microstructures and microwave dielectric properties of ZnNiTiO 4 ceramics

Intrinsic dielectric behavior of Mg 2 TiO 4 spinel ceramic

Crystal structure and microwave dielectric properties of Mg 2 Ti 1-x Ga 4/3x O 4 (0.05 ≤ x ≤ 0.13) ceramics

Microstructures and microwave Mater

Influence of Sn-substitution on microstructure and microwave dielectric properties of Na 1/2 Nd 1/2 TiO 3 ceramics

Effects of Zr-substitution on Mater

Microwave dielectric properties of Na 1/2 Sm 1/2 Ti 1−x (Cr 1/2 Nb 1/2 ) x O 3 Ceramics (x = 0-0.025)

Sintering characteristics and microwave dielectric properties of

Structural transitions and microwave dielectric properties of Ba 2−2x Sr 2x SmSbO 6 double perovskites

Structure stability and microwave dielectric properties of double perovskite ceramics-Ba 2 Mg 1−x Ca x WO 6 (0.0≤ x ≤ 0.15)

Effect of sintering temperature on microstructures and microwave dielectric properties of Ba 2 MgWO 6 ceramics

First-principle calculation and assignment for vibrational spectra of Ba(Mg 1/2 W 1/2 )O 3 microwave dielectric ceramic

Dielectric properties of CaCu 3 Ti 4 O 12 , Ba(Fe 1/2 Nb 1/2 )O 3 , and Sr(Fe 1/2 Nb 1/2 )O 3 giant permittivity ceramics at microwave frequencies

Effect of Bi 2 O 3 and B 2 O 3 additives on the sintering temperature, microstructure, and microwave dielectric properties for Sm(Mg 0.5 Ti 0.5 )O 3 ceramics

New dielectric material system of Nd(Mg 1/2 Ti 1/2 )O 3 -SrTiO 3 in the microwave frequency range

Improving microwave dielectric properties of La 2.98/3 Sr 0.01 (Mg 0.5 Sn 0.5 )O 3 ceramics with CuO additive

Microwave dielectric properties of Nd(Zn 1/2 Ti 1/2 )O 3 ceramics with V 2 O 5 additives

Effect of Sm substitution on microwave dielectric properties of Nd(Mg 0.5 Sn 0.5 )O 3 ceramics

Microwave dielectric properties and microstructures of Nd(Mg 0.5−x Co x Sn 0.5 )O 3 ceramics

Enhancing the microwave dielectric properties of Nd(Mg 0.5 Sn 0.5 )O 3 ceramics by substituting Nd 3+ with Ca 2+

Effect of Sr substitution on microwave dielectric properties of Nd(Mg 0.5 Sn 0.5 )O 3 ceramics

Influence of Ba 2+ substitution on the microwave dielectric properties of Nd(Mg 0.5 Sn 0.5 )O 3 ceramics

Improved microwave dielectric properties of Nd(Mg 0.5 Sn 0.5 )O 3 ceramics with Ni 2+ substituting

Improved microwave dielectric properties of Nd(Mg 0.5 Sn 0.5 )O 3 ceramics by substituting Mg 2+ with Zn 2+

Microwave dielectric properties and microstructures of Nd(Mg 0.5 Sn 0.5−x Ti x )O 3 ceramics

A hybrid dielectric resonator antenna based upon novel complex perovskite microwave ceramic

Microwave dielectric properties of Nd[(Zn 1−x Co x ) 0

Influence of Zn nonstoichiometry on the phase structure, microstructure and microwave dielectric properties of Nd(Zn 0.5 Ti 0.5 )O 3 ceramics

Lattice vibrational characteristics, crystal structures and dielectric properties of non-stoichiometric Nd (1+x) (Mg 1/2 Sn 1/2 )O 3 ceramics

Lattice vibrational characteristics and structures-properties relationships of non-stoichiometric Nd

Microstructures and microwave dielectric properties of La 1-x B x (Mg 0.5 Sn 0.5 )O 3 ceramics

Improved microwave dielectric properties of La(Mg 0.5 Sn 0.5 )O 3 ceramics with Yb 3+ doping

Improved microwave dielectric properties of La(Mg 0.5 Sn 0.5 )O 3 ceramic with Ba 2+ substitution

Dielectric and optical properties of ZnO and Eu 2 O 3 doped Pr 0.22 Y 0.78 TiTaO 6 ceramic

Tuning the microwave dielectric properties of La(Mg 0.4 Sr 0.1 Sn 0.5 )O 3 by introducing Ca 0.8 Sr 0.2 TiO 3

Microwave dielectric properties of (1−x)Nd(Co 1/2 Ti 1/2 )O 3 -x(Ca 0.8 Sr 0.2 )TiO 3 composite ceramics

Improved microwave dielectric properties of La(Mg 0.5 Sn 0.5 )O 3 ceramic with Sr 2+ Substitution

Microwave dielectric properties of (1−x)Ca 0.6 La 0.267 TiO 3 −xCa

Lattice structure and microwave

Vibrational spectroscopic and crystal chemical analyses of double perovskite Y 2 MgTiO 6 microwave dielectric ceramics

Structure and microwave dielectric property relations in Barium cobalt magnesium niobate ceramics

Microwave dielectric properties of multi-ions Ba(Zn,Ta)O 3 -based perovskite ceramics

Raman scattering, electronic structure and microwave dielectric properties of Ba

Effect of small amount of cobalt substitution on structure and microwave dielectric properties of Barium magnesium niobate ceramics

Effects of postdensification annealing on microwave dielectric properties of Ba

Effects of postdensification annealing upon microstructures and microwave dielectric characteristics in Ba((Co 0.6−x/2 Zn 0.4−x/2 Mg x ) 1/3 Nb 2/3 )O 3 ceramics

Effects of Mg substitution on order/disorder transition, microstructure, and microwave dielectric characteristics of Ba((Co 0.6 Zn 0.4 ) 1/3 Nb 2/3 )O 3 complex perovskite ceramics

Effect of sintering temperature on dielectric properties, vibrational modes and crystal structures of Ba

Effects of Ba deficiency on ion ordering, grain growth, and microwave dielectric properties of Ba 1-x Zn 1/3 Nb 2/3 O 3 ceramics

Correlation among dielectric properties, vibrational modes, and crystal structures in Ba[Sn x Zn (1-x)/3 Nb 2(1-x)/3 ]O 3 solid solutions

Evaluation of dielectric properties, vibration modes, and crystal structures in Ba

Abnormal variation of microwave dielectric properties in A/B site co-substituted (Ca 1−0.3x La 0.2x )[(Mg 1/3 Ta 2/3 ) 1−x Ti x ]O 3 complex perovskite ceramics

Structure and microwave dielectric properties of Ba

Influence of sintering temperature on microwave dielectric properties, structure and lattice modes of Ba(Zn 1/3 Ta 2/3 )O 3 resonators

Improvement of microwave dielectric properties for Ba

Zr-substitution

Tailoring the order-disorder transition

Low loss (Ba 1−x Sr x )(Co 1/3 Nb 2/3 )O 3 solid solution: Phase evolution, microstructure and microwave dielectric properties

Effects of Y 2 O 3 substitution on microwave dielectric properties of Ba(Co 0.6 Zn 0.38 ) 1/3 Nb 2/3 O 3 ceramics

Effects of Y 2 O 3 /CeO 2 co-doping on microwave dielectric properties of Ba(Co 0.6 Zn 38 ) 1/3 Nb 2/3 O 3 ceramics

Structural ordering and dielectric properties of Ba 3 CaNb 2 O 9 -based microwave ceramics

Ultra-high-Q and wide temperature stable Ba(Mg 1/3 Ta x )O 3 microwave dielectric ceramic for 5G-oriented dielectric duplexer adhibition

Microwave dielectric properties of Ba(Zn 1/3 Ta 2/3 )O 3 ceramics doped with Nb 2 O 5 , MnO 2 or V 2 O 3

Sintering characteristics and microwave dielectric properties of Ba(Co 1/3 Nb 2/3 )O 3 -MnO 2 ceramics

Microwave dielectric properties of Ba(Co 0.56 Y 0.04 Zn 0.35 ) 1/3 Nb 2/3+x O 3 (x = −0.004 ~ 0.008) ceramics

Microwave dielectric properties of Ba(Zn 1/3 Ta 2/3 )O 3 for application in high power waveguide window

Microstructure and microwave dielectric properties of Ba([Mg 1−x Zn x ] 1/3 Ta 2/3 )O 3 solid solution ceramics

Effect of La 2 O 3 addition on the microwave dielectric properties of Ba(Mg 1/3 Ta 2/3 )O 3 ceramics

Influence of Ca 2+ substitution for Ba 2+ on the crystal structure and microwave dielectric properties of Ba 1−x Ca x (Mg 1/3 Ta 2/3 )O 3 ceramics

Microwave dielectric properties of Ba[Mg 1−x/3 Sn x Ta 2(1−x)/3 ]O 3 (x = 0-0.25) ceramics

Wide temperature stable Ba(Mg x Ta 2/3 )O 3 microwave dielectric ceramics with ultra-high-Q applied for 5G dielectric filter

Crystal structure of Ca 5 Nb 5 O 17

Structure and microwave dielectric properties of Ca 5 A 4 TiO 17 (A = Nb, Ta) ceramics

Influence of Sm substitution on the phase, microstructure and microwave dielectric properties of SrLa 4 Ti 5 O 17

Low loss Sr 1−x Ca x La 4 Ti 5 O 17 microwave dielectric ceramics

Phase, microstructure and microwave dielectric properties of Zr-doped SrLa 4 Ti 5−x Zr x O 17

Microwave dielectric properties of CaO-La 2 O 3 -Nb 2 O 5 -TiO 2 ceramics

Microwave dielectric properties of La 3 Ti 2 TaO 11 ceramics with perovskite-like layered structure

The effect of processing conditions on the phase, microstructure and dielectric properties of SrCa 4 Nb 4 TiO 17 and Ca 5 Nb 4 TiO 17 microwave ceramics

Phase, microstructure, and microwave dielectric properties of NaCa 4−x Sr x Nb 5 O 17 (x = 0 to 4) ceramics

Preparation and characterization of K-substituted NaCa 4 Nb 5 O 17 microwave dielectric ceramics

Ca 4 La 2 Ti 5 O 17 : A novel low loss dielectric ceramics in the CaO-La 2 O 3 -TiO 2 system

Microwave dielectric properties of Ca 4 La 2 Ti 5−x (Mg 1/3 Nb 2/3 ) x O 17 ceramics

Low loss and middle permittivity of (1−x)Ca 4 La 2 Ti 5 O 17-x NdAlO 3 dielectric resonators with near-zero temperature coefficient of the resonant frequency

Synthesis, microstructure and microwave dielectric properties of Ca 4-x Mg x La 2 Ti 5 O 17 ceramics

Sr 4−m La m Ti m−1 Ta 4−m O 12 (m = 1, 2, 3): A novel series of A 4 B 3 O 12 -type microwave ceramics with a high Q and low τ f

Two novel A 4 B 3 O 12 -type microwave ceramics with high-Q and near-zero τ f

Structural, spectroscopic and dielectric investigations on Ba 8 Zn(Nb 6-x Sb x )O 24 microwave ceramics

Structural analysis and properties of thermally stable Ba 8 Mg(Nb 6-x Sb x )O 24 microwave ceramics

Synthesis, structural analysis and dielectric properties of Ba 8 (Mg 1-x Zn x )Nb 6 O 24 hexagonal perovskites

Phase structure, band gap and microwave dielectric properties of Ba 8 Ti 3 Nb 4−x Sb x O 24 ceramics

Microstructures and microwave dielectric properties of Ba 4 LiNb 3 O 12 -BaWO 4 composite ceramics

Ba 4 LiNb 3−x Sb x O 12 : Phase evolution, microstructure and optimized microwave dielectric properties

Phase transformation and microwave dielectric properties of Ba 4 LiTa 3−x Sb x O 12

Effect of Sb 5+ substitution on the dielectric properties of Ba 3 LiTa 3 Ti 5 O 21 ceramics

Microwave dielectric properties of Ba 3 LiNb 3−x Sb x Ti 5 O 21

High ε r and low loss microwave dielectric ceramics Ba 3 LiNb 3−x Ta x Ti 5 O 21

Microwave dielectric properties of LiSmTa 4 O 12 ceramics with A-site deficient perovskite structure

Structural dependence of microwave dielectric properties of SrRAlO 4 (R = Sm

Microstructures and microwave dielectric properties of the CaSmAlO 4 -based ceramics

Structure and microwave dielectric characteristics of Ca 1+x Nd 1−x Al 1−x Ti x O 4 ceramics

Effect of A-site ionic radius on the structure and microwave dielectric characteristics of Sr 1+x Sm 1−x Al 1−x Ti x O 4 ceramics

Improvement of microwave dielectric characteristics in SrNdAlO 4 ceramics by Ca-substitution

Microstructures and microwave dielectric characteristics of CaRAlO 4 (R = Nd, Sm, Y) ceramics with tetragonal K 2 NiF 4 structure

Infrared reflectivity spectra and microwave dielectric properties of (Sr 1−x Ca x )SmAlO 4 (0 ≤ x ≤ 1) ceramics

Structure and microwave dielectric properties of solid solution in SrLaAlO 4 -Sr 2 TiO 4 system

Structural evolution and its effects on dielectric loss in Sr 1+x Sm 1−x Al 1−x Ti x O 4 microwave dielectric ceramics

Structure and microwave dielectric properties of SrSmAlO 4 -Sr 2 TiO 4 solid solutions

Structural evolution of SrLaAl 1-x (Zn 0.5 Ti 0.5 ) x O 4 ceramics and effects on their microwave dielectric properties

Zn) microwave dielectric ceramics with complex K 2 NiF 4 -type layered perovskite structure

Microwave dielectric properties of SrLa

Tailoring the microwave dielectric properties of Sr 0.6 Ca 0.4 LaAlO 4 ceramic by TiO 2 addition

Sr n+1 Ti n O 3n+1 (n = 1, 2) microwave dielectric ceramics with medium dielectric constant and ultra-low dielectric loss

Structure and microwave dielectric characteristics of Sr(La 1-x Sm x ) 2 Al 2 O 7 ceramics

Sr 2 LaAlTiO 7 : A new Ruddlesden-Popper compound with excellent microwave dielectric properties

Structure evolution and enhanced microwave dielectric characteristics of (Sr 1−x Ca x )La 2 Al 2 O 7 ceramics

SrLn 2 Al 2 O 7 (Ln = La, Nd, Sm) microwave dielectric ceramic new materials

Synthesis and μ-Raman scattering of Ruddlesden-Popper ceramics Sr 3 Ti 2 O 7 , SrLa 2 Al 2 O 7 and Sr 2 LaAlTiO 7

Sr 1-x Ca x ) 2 TiO 4 microwave dielectric ceramics with R-P structure (x = 0-0.15)

Structural evolution and microwave dielectric properties in Sr 2 (Ti 1-x Sn x )O 4 ceramics

Structure and microwave dielectric characteristics of Sr 2

Improved microwave dielectric properties of the (Sr 1−3x/2 La x ) 2 Ti 1−y Ce y O 4 ceramics

A novel ultralow-loss Sr 2 CeO 4 microwave dielectric ceramic and its property modification

Ce 0.75 Y 0.25 O 1.875 : New temperature-stable microwave dielectric ceramics with high Q values for microwave application

Microwave dielectric properties of Bi 2 (Li 0.5 Ta 1.5 )O 7 -TiO 2 -based ceramics for 5G cellular base station resonator application

Structures and microwave dielectric properties of Ti-doped CeO 2 ceramics with a near-zero temperature coefficient of resonant frequency

Dielectric resonator antennas based on high quality factor MgAl 2 O 4 transparent dielectric ceramics

The structure evolution

Vibrational spectroscopy and microwave dielectric properties of two novel Ca 3 Ln 2 W 2 O 12 (Ln = La, Sm) tungstate ceramics

Phase structure, sintering behaviour and microwave dielectric properties of Ln 2 MoO 6 (Ln = La and Y) ceramics

Virtual screening of inorganic materials synthesis parameters with deep learning

Machinelearning-assisted materials discovery using failed experiments

Simple descriptor derived from symbolic regression accelerating the discovery of new perovskite catalysts

Machine learning assisted predictions of intrinsic dielectric breakdown strength of ABX 3 perovskites

Accelerated search for BaTiO 3 -based piezoelectrics with vertical morphotropic phase boundary using Bayesian learning

Machine learning approach for prediction and understanding of glass-forming ability

From organized high-throughput data to phenomenological theory using machine learning: The example of dielectric breakdown

Machine learning approaches for permittivity prediction and rational design of microwave dielectric ceramics

Structure and microwave dielectric properties of gillespite-type ACuSi 4 O 10 (A = Ca, Sr, Ba) ceramics and quantitative prediction of the Q × f value via machine learning

This work is supported by the National Natural Science Foundation of China (Grant No. 51872037).

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