Mechanical Alloying and Spark Plasma Sintering of Higher
Manganese Silicides for Thermoelectric Applications

YATIR SADIA,1,2 LIRON DINNERMAN,1 and YANIV GELBSTEIN1

1.—Department of Materials Engineering, Ben-Gurion University of the Negev, Beer Sheva,
Israel. 2.—e-mail: yatttir@yahoo.com

The present challenges in the energy crisis require finding new ways to reduce
consumption of fossil fuels. Thermoelectrics can help reduce fuel consumption
by producing electricity from waste heat. The higher manganese silicides
(HMS) have shown promise in this field as inexpensive, nontoxic, and highly
stable p-type thermoelectric materials. One of the production techniques for
HMS is mechanical alloying by ball milling. In this research the effect of the
ball-milling duration and speed on the phases produced was studied. Mn and
Si powders were milled at speeds of 200 RPM to 800 RPM for 1 h to 7 h. X-ray
diffraction (XRD) results of the samples prepared using mechanical alloying
show deterioration into the MnSi phase. The sample that underwent 5 h of
milling at 800 RPM showed the greatest amount of HMS phase and was
subsequently spark plasma sintered. The sample showed insufficient ther-
moelectric properties (ZT � 0.1 at 450�C), compared with either solid-state
reaction samples showing ZT � 0.4 or cast samples showing ZT � 0.63 at
450�C. The reduced ZT values of the mechanically alloyed and spark-plasma-
sintered samples were attributed to the high relative amount of MnSi phase.
The correlation between the relative amount of MnSi and the transport
properties is described in detail.

Key words: Higher manganese silicides, thermoelectric, mechanical
alloying, spark plasma sintering

INTRODUCTION

In the past few years, rising fossil fuel prices and
greenhouse effects have shifted the world view on
renewable energy sources. While various methods of
energy conversion exist, one of the most exciting
is thermoelectric technology, which satisfies the
requirements for long-term stability and low main-
tenance. This is made possible due to the fact that
thermoelectric systems have no moving parts. One
of the most important measures of the efficiency of a
thermoelectric material is the dimensionless figure
of merit (ZT), defined as the square of the Seebeck
coefficient times the temperature over the electrical
resistivity times the thermal conductivity. While
various materials possess desired properties for

thermoelectric performance, chalcogenides such as
bismuth telluride, germanium telluride, and lead
telluride mainly dominated the field in the past.
However, while the thermoelectric properties of
chalcogenides result in high figure-of-merit values,
they have not been successfully introduced into
mass production, being limited to rather minor,
specialized applications. This has been due to some
of their other characteristics, including inferior
mechanical properties, toxic lead content, high price
of base materials, and high vapor pressure at their
peak efficiency temperatures.

In the past few years, several materials have
shown thermoelectric properties comparable to those
of the chalcogenides. Such families of materials
include skutterudites, half-Heuslers, and metal sili-
cides. While all of these material classes have specific
merits, metal silicides have attracted much attention
due to their low materials cost, high chemical and

(Received June 18, 2012; accepted January 7, 2013;
published online February 20, 2013)

Journal of ELECTRONIC MATERIALS, Vol. 42, No. 7, 2013

DOI: 10.1007/s11664-013-2476-4
� 2013

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