Seebeck Coefficient and Electrical Resistivity of Some Rare Earth Ternary Sulfides La/sub 3-x/M/sub x/S sub 4 (M = Sm, Eu, Yb)

摘要

Binary lanthanum sulfides with compositions between La sub 2 S sub 3 and La sub 3 S sub 4 form a continuous series of solid solutions in the high temperature gamma form and have been reported to have high figures of merit. In this study, in order to achieve increased stability of the gamma form, compounds with the formula La/sub 3-x/M/sub x/S sub 4 (M = Sm, Eu, Tb and x = 0.1 to 0.9) were prepared. The Seebeck coefficients and electrical resistivities of these ternary sulfides are reported as well as some preliminary results on their long term thermal stability. The compounds La/sub 3-x/M/sub x/S sub 4 (M = Sm, Eu, Yb and x = 0.1 to 0.9) prepared in this study all possessed the high temperature gamma -Th sub 3 P sub 4 structure and the compounds with small values of x possessed attractive thermoelectric properties. The figure of merit at 1000 deg C of these compounds is in the neighborhood of 0.7 to 0.8 x 10 sup -3 deg C sup -1 when the thermal conductivity is taken to be 15 mW deg C sup -1 cm sup -1 and is comparable to that of binary LaS/sub x/ and SiGe alloys. Long term vaporiation data indicate that these materials are stable in vacuum for an extended period of time. 12 refs., 4 figs., 1 tab. (ERA citation 11:036117)