Thermoelectric properties of Zn-In complex chalcogenides

A ceramic compact of ZnIn₂S₄ with spinel structure and another polymorphism of ZnIn₂S₄ with a layer structure known as IIIa phase were synthesized by reaction-sintering of the mixed powder of ZnS and In₂S₃ at 450°C and 800°C under Ar (containing 1% H₂) atmosphere, respectively. Their thermoelectric properties were investigated in the temperature range from 200° to 600°C. Power factor of IIIa type was much larger than that of the spinel type, although it was slightly lower than maximum power factor of the oxide homologous compounds ((ZnO)_mIn₂O₃). To increase the thermoelectric properties of ZnIn₂S₄ a c-plane oriented sintered body of IIIa phase was successfully fabricated by a usual ceramic process. The power factor in the direction perpendicular to c-axis was larger than that in the direction parallel to c-axis due to higher electrical conductivity in the former direction