The purpose of this work was to determine the thermoelectric properties of the pseudobinary system MgfSi-MgfGe. The compositions investigated were Mg2Si, Mg2Ge0.fSi0.s, MgaGe0.4Si0.6, Mg2Ge0.6Si0.4, Mg2Ge0.8Si0.2, and Mg2Ge. X-ray diffraction lattice parameter measurements and differential thermal analysis measurements established the existence of complete solid solubility between Mg~Si and Mg2Ge. Both the lattice parameter and liquidus temperature show almost linear variation with composition in this system. The melting temperature of MgfSi was found to be 1070" ___ 5"C, while that of MgfGe was found to be 1102" _ 5~Electrical resistivity and Hall effect measurements indicated that at 300*K the electron Hall mobility in the mixed crystals is essentially the same as that of the pure compounds. Maximum values obtained were slightly above 300 cm2/volt sec. The forbidden energy gap appeared to vary monotonically from about 0.78 electronvolt (ev) for MgfSi to about 0.70 ev for MgfGe. Thermal conductivity measurements on the pseudobinary system showed that the lattice thermal conductivity of the solid solutions is substantially lower than that of either of the pure compounds at 300~ At this temperature the lattice thermal conductivity of Mg2Ge0.6Sio.4 was found to be 0.0268 watt/cm *K. The maximum thermoelectric figure of merit which could be obtained with these materials is not as good as that of other materials now in use.

The thermal conductivities of relatively large homogeneous samples of Mg2Si and Mg2Ge have been measured in a dynamic calorimeter from 0~ to 300~ In both samples, phonon scattering predominates, and the relationship, kT ~ constant was observed. For Mg2Si, kT ~ 23.4 watts/cm, and for Mg2Ge, ~T -~ 19.8 watts/cm. Although the electrical properties of Mg2Si and Mg2Ge have been measured by several investigators (1-5), the thermoelectric figure of merit for the materials could not be determined because their 1 Present address: Advanced Development Section, Liquid Rocket Plant, Aerojet-General Corporation, Sacramento, California.thermal conductivities had not been measured. In this paper, the results of thermal conductivity measurements made on Mg2Si and Mg2Ge in a dynamic calorimeter are presented.The method which has been used to measure the thermal conductivity is an extensive modification ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 128.193.164.203 Downloaded on 2014-06-24 to IP

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