Thermoelectric Properties of Re3Ge0.6As6.4 and Re3GeAs6 in Comparison to Mo3Sb5.4Te1.6

Heavily doped narrow gap semiconductors with complex crystal structures are prime candidates for thermoelectric materials. The arsenides Re3(Ge,As)7 are new examples with promising thermoelectric properties, comparable with the isostructural Mo3Sb5.4Te1.6, a competitive high-temperature material. Various doping levels may be achieved by using different Ge/As ratios. Re3(Ge,As)7 was prepared by heating the elements in the desired ratios in evacuated silica tubes between 600 and 800 °C. Re3GeAs6 crystallizes in the cubic Ir3Ge7 type, space group Im3m, with a = 8.73202(8) A. It exhibits high Seebeck coefficient, high electrical conductivity, and reasonably low thermal conductivity. Moreover, the thermoelectric figure-of-merit ZT = TS2σ/κ increases rapidly with increasing temperature, as desired for high-temperature thermoelectrics.