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 Re-3(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. Re-3(Ge,As)(7) was prepared by heating the elements in the desired ratios in evacuated silica tubes between 600 and 800 degrees C. Re3GeAs6 crystallizes in the cubic Ir3Ge7 type, space group Im $$($) over barm, 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 = TS2 sigma/kappa increases rapidly with increasing temperature, as desired for high-temperature thermoelectrics.