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MICROCOPY RESOLUTION TEST CHART
NATIONAL BUREAU OF STANDARDS – 1963
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ErO(OH) – A Monoclinic Lanthanide Oxyhydroxide*
RELEASED FOR ANNOUNCEMENT
IN NUCLEAR SCIENCE ABSTRACTS
by 0. C. Kopp and L. A. Barris
Metals and Ceramics Division, Oak Ridge National laboratory
Cak Ridge, Tennessee 37831
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*Research sponsored by the U.S. Atomic Energy Commission under
contract with the Union Carbide Corporation.
The writers are respectively, consultant to the Metals and Ceramics
Division from the Department of Geology and Geography, University of
Tennessee, Knoxville, Tennessee, and member of the research staff, Metals
and Ceramics Division, Oak Ridge National Laboratory.
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ABSTRACT
single crystals of hydrothermally synthesized Ex'O(OH) bave
monoclinic symmetry. Frevious investigators have considered related
lanthanide oxyhydroxides of Yb and Eu to be orthorhombic based on
powder diffraction data. The unit cell has dimensions: A. = 4.299
+ 0.005A, B = 3.601 + 0.002A, S. = 11.225 + 0.005A, B = 92°08' + 0°06'.
Twinning is common with (001) as both the twin and composition plares.
Chemical, physical and optical data are presented.
Introduction
Although the lanthanide oxyhydroxides have been known to exist
for some time, -,2 their structures have not been adequately determined.
Fricke and Dirri&coters indicate that they obtained a single-crystal
rotation photograph from a psevdomorph or ErO(OH) which was obtained
by heating a crystal of Fr(OH).,; however, no data was reported from
this experiment. In the same paper Fricke and Dirrwechter present
tentative lattice parameters for YnO(OH) based on analysis of powder
diffraction data. Shafer and Roy* synthesized oxyhyüroxides of Sm,
Nd, Y, and possibly La; they suggest that these compounds are iscmorphous
based on powder diffraction data.
More recent.ly, Rau? studied the europium oxides and bydroxides,
but was not able to obtain large enough crystals of either Eu(OH)2
or EuO(OH) for single-crystal studies. While Rau attempted to index
the powder pattern of E10(OH) on the basis of an orthorhombic cell sọ
that the lattice parameters could be determined, he notes that the
cell chosen is probably a pseudo cell end that additional data,
preferably from single crystals, would be needed to positively describe
Eu0(08).
In the present investigation crystals of hydrothermally grown
Ero(CH) have been studied by the x-ray powder method and by rotation,
Weissenberg and precession methods. The powder patterns of Ero(OH)
and EuO(OH) are virtually identical, but the single crystal data
pı ve Ero(OH) to be monoclinic rather than orthorhombic.
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Synthesis of Ero(OH)
Crystals of Ero(OH) up to 2.5 mm long have been grows bydro-
thermally from the system Er, 02-L10H-1.0 10 the temperature range
320-420°C and the pressure range 9000-22,000 psi. The largest
crystals were obtained under the following conditions:
Nutrient:
Er Oą powder (99.9%, Fairmount Chemical
Company)
Seeds:
Hone - spontaneous nucleatiou in cooler region
Solvent:
2.5 N LICH
Upper temperature: 405 + 5°C
Base temperature: 420 + 8°C
Pressure:
12,000 £ 500 pis1
347 stainless steel
Liner:
Duration:
Three weeks
The Ero(OH) crystals obtained in these experiments are pink, ·
have a hardness of about 4 Mohs) and have generally a prismatic
habit. The characteristic color and habit of the crystals made
possible the separation of the oxyhydroxide from other phases such
a8 ErFe0g. Data taken from Debye-Scherrer flims of ErooH) were
compared with data for YO(OH)4 and Euo(0H)) and shown to give good!
agreements (Table 1). The indexing of our pattern is based upon the
results of single-crystal measurements described in a later section.
Corroboration of the identification of the phase as Ero(OH) was
made by spectrographic analysis and weight loss determination.
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Table I. Comparison of X-ray Data
Ero(OH)
_E_O(OH)
A hike
dA
bike
5.602
4.058
3.948
002
101
101
020
200
121
5.78
4.109
4.016
--
3.142
2.934
2.892
--
_YO(OR)_
DA I
5.671 90
4.076 80
3.986 95
3.547 10
3.064
2.891 100
2.822 55
2.783
2.714 05
2.690
15
022
103
022
S
222
004
040
3.038
2.872
2.796
2.769
2.696
2.670
2.217
ů
103
2.837
voob ü ü i wo T ☺
230
M
111
111
111
113,014
2.225
2.761
2.744
2.288
2,258
2.168
2.062
202
300,140
042,023
241,232
312
322, 400
MW
55
200
202,105
30
202
2.000
MS
S
u
2.145
2.026
1.977
1.8.
1,811
1.764
1..734
1.722
1.673
1,650
2.151
2.033
1.987
1.878
1.820
1.773
1.739
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05
15
006
020
115
212,204
115,022
204
. 121, 121
1.932
1.874
2.810
1.771
to
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M
v
Br,W
15
1.699
1.677
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Table I continued
De bye-Scherrer camera, 214.59 diam, cuk, radiation, Ni filter,
(1 = 1..5418A). V8 = very strong, 8 = strong, MS - medium strong,
M = medium, MW = mediom weak, W = weak, WW - very weak, f = faint,
Br = broad.
shafer and Roy, see reference 4. Although yttrium is not one of the
lanthanides, its ionic size and properties are very close to those
of dysproeium and holmium.
see reference 5.
Indexed on the basis of an assured orthorhaubic
cell, with a = 8.235A, b. = 11.626A, and c. = 7.453A.
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Spectrographic analysis indicates that only the following impurities
are present in detectable amounts (in weight percent): Ca - 0.0053
Cu ~ 0.0005Fe - 0.01; L1 -0.002; Mn - 0.0023 81 - 0.02. The
reasonably high purity of those crystals in spite of grovih in a
steel liner with an alkaline solvent may be partly due to the
s luultaneous growth of ErFeOg, which is thought to take up not oniy
the iron but other metallic impurities.
The second confirmatory analysis was made by theru:ally decomposing
the compound and determining its weight loss during hexiting. The
compound started to decompose at 330 + 25°C which agrees with the
decomposition temperature (320°c) reported by Fricke and Seltz.?
The total determined weight loss (4.50 + 0.30%) equals the theoretical
weight 1068 (4.50%) for the reaction:
2Ero(OH) → Erzº3 + H2O
After beating, the residue 18 Er202 based on its x-ray powder pattern.
No other phases were observed. By way of comparison, Er(CH), loses
12.2% of its original weight when converted to Er,0by heating.
Optical Properties of Ero(OH)
Since the beta angle is 92.08' and there 18 a perfect (001)
cleavage, the optical characteristics of Ero(OH) can be easily
mistaken for those of orthorhombic materials. Figure 1 11lustrates
the relations between the crystallograpbic and optical axes. The
optical properties (determined with white light) are summarized in
Table II. The index , was difficult to measure because the cleavage
tends to almost invariably yield nearly centered acute bisectrix.
figures. Other cleavage directions - (010), (100) and possibly
Table II. Optical Properties of Ern(OH)
Optic sign
2
y
श्री प्री श्री
Biaxial (-)
Low (about 15°)
1.79 1 0.01
1.88 0.01
, 1.89 + 0.01
Approximately || (100)
Approximately || a-ards
Parallel to trace of a-
and b-axes in başal section
Strong (v >r)
Optic plane
Optic normal
Extinction
Dispersian
a prismatic type (bko) appear to be developed and their traces are
visible with the microscope.
Single Crystal Diffraction Data
Crystallographic data obtained from single rystals of Ero(OH)
are presented in Table III. Rotation, Weissenberg and precession
X-ray dific'action methods were used with Cuk, (i = 1.5418A) and
MOK, (i = 0.71078) radiations.
The twinning relationships could be deduced from the doubling
of the diffraction spots observed on Weissenberg 111ms obtained from
an apparent single crystal rotated about its b-axis. Only reflections
of the type 001, ool, Okl, and Ok I appeared as cingle diffraction
spots. The composition and twin plane is the (001) plane. The twin
bears a close resemblance to the Mane bach twin of the mineral
orthoclase.
Discussion and Conclusions
Insofar as the authors have been able to determine, the lanthanide
rare-earth oxylydroxides were considered to be orthorbombic by
earlier workers, but this conclusion was based almost entirely on
powder diffraction data. single crystal X-ray diffraction studies
have revealed that Ero(OH) 18 monoclinic rather than orthorbombic.
It is possible that polymorphism exists for Ero(OH) such that both
monoclinic and orthorhombic forms exist. The close agreement of
X-ray powder data and thermal decomposition data does not favor this
possibility, but does not preclude it. The existence of an
orthorhombic form of ErO(OH) would need to be confirmed by study of
single crystals.
Table III. Single-Crystal Data for Ero(ok)
= 4.299 + 0.005A
= 3.601 0.002A
= 11.225 + 0.005A
* 92°08' 1 0:06'
X-ray density
= 7.66 g/cm3
Molecw.es per wit cell - 4
Space group
= P21/A (second setting)
Parameters were measured from photographs calibrated
with the diffraction pattera of powdered silver.
The measured density determined on a small (about
26 mg) sample was 7.3 using a weight-loss-11-
water technique. The crystals used contain some
liquid inclusions visible at 20x which may account
for the lower density value than determined by
X-ray means. However, the value appears to be
sufficiently accurate to determine the number of
molecules per unit cell.
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The lonic radius of Er*3 is considered to be 0.89A which 18
near the lower size limit of the rare-earth trivalent ions (largest -
La*3 = 1.14A, smallest – Lu*3 = 0.85A) according to Ahrens. Whether
other lanthanide oxyhydroxides are monoclinic is the subject of a study
now in progress.
Acknowledgements
The authors are grateful to A. T. Chapman of the Oak Ridge
National Laboratory for determining the weight loss of the Ero(OH)
compound during heating. We also wish to thank H. L. Yakel and
J. H. Burns of the Oak Ridge National Laboratory for their critical
reading of the manuscript and their helpful suggestions.
11
1. G. F. Auttig and M. Kantor, "Oxyhydrates and Active Oxides. XIIX.
The System Ianthanum(III)oxide Water," z. anorg. Chemie, 202,
421-428 (1931)(in German).
R. Fricke and A. Seitz, "Crystalline Hydroxides of the Rare Earths,"
Z. anorg. Coemie, 354, 107–115 (1947)(in German).
3. R. Fricke and W. Dürrwachter, "Further studies on Crystalline Rare-
Earth Hydroxides," z. anorg. Chemie, 359, 305–308 (1949)(in German).
M. W. Shafer and R. Roy, "Rare-Earth Polymorphism and Phase Equi-
libria in Rare-Earth Oxide-Water Systems," J. Am. Ceram. Soc. 42,
[11], 563–570 (1959).
5. R. C. Rau, "X-ray Crystallographic studies of Europium Oxides and
Hydroxides," pp. 117–134 in Rare Earth Research II, p. 621,
Karl S. Vorres, editor, Gordon and Breach Science Publishers,
New York, 1964.
6. A. N. Winchell and H. Winchell, Elements of Optical Mineralogy, ;
Part II. Descriptions of Minerals, 4th ed., M.551, John Wiley
and Sons, New York, 1951.
7. L. H. Ahrens, "The Use of Ionization Potentials. Part I. Ionic
Radii of the Elements," Geochim. et Cosmochim. Acta, 2, 155–169
(1952).
Fig. 1. Relationship of Optical and Cryɛtallographic Axes in
ErO(OH) Observed in a Cleavage Flake (001).
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Figol. Relationship of optical and Crystallographic
cxes in E1066) sean in a cleavage flabre
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