SEMICONDUCTING MATERIALS FOR THERMOELECTRIC POWER GENERATION

Abstract

Thermoelectric properties of semiconductors suggest that (1) this class of materials can be useful in powergenerating thermocouples operating at least up to 700 deg C, and (2) use of a sandwich-type arrangement or graded alloying in the construction of thermocouple branches will be necessary to achieve high figures of merit over a wide temperature range and, hence, high power-generating efficiencies. Ternary compound semiconductors having the cubic structure were synthesized. Those with the rock-salt structure, such as AgSbTe/sub 2/, are characterized by low lattice thermal conductivities (<0.0075 watt cm/sup -1/ deg/ sup -1/). The lattice thermal conductivity as a function of composition was examined in the alloy systems of AgSbTe/sub 2/ with PbTe, SnTe, and GeTe. The minimum in the lattice thermal conductivity for the AgSbTe/sub 2/ -- PbTe system gives an effective mean free path for phonons which is less than unit-cell dimensions. Measurements of the temperature dependence of thermoelectric properties of a number of solid-solution alloy systems showed that (1) solid- solution ulloys of Bi/sub 2/Te/sub 3/, with Bi/sub 2/Se/sub 3/, Sb/sub 2/Te/sub 3/ , and Sb/sub 2/Se/sub 3/ provided the best p- and ntype material for thermocouple operation at 25 to 250 deg C, (2) the ternary compoundmore » AgSbTe/sub 2/ and its alloys with GeTe provided the best p-type material at 250 to 550 deg C, and (3) alloys in the PbTe-- SnTe system provided the best n-type material at 250 to 550 deg C. Power-generating thermocouples, constructed in the sandwich-type arrangement of materials, provided an efficiency of approximately -12 per cent for operation at 20 to 550 deg C (i.e., TH -- TC = 530 deg C). Continuous thermocouple operation for 300 hours resulted in no significant deterioration of material properties. (auth)« less