On the Electrical and Thermal Properties of the Ternary Chalcogenides A2 IBIVX3, AIBVX2 and A3 IBVX4 (AI=Cu; BIV=Ge, Sn; BV=Sb; X=S, Se, Te). I. Thermoelectric Properties at Room Temperature

Electrical conductivity, Seebeck coefficient, thermal conductivity and microhardness of ternary chalcogenides A2 IBIVX3, AIBVX2 and A3 IBVX4 (AI=Cu; BIV=Ge, Sn; BV=Sb; X=S, Se, Te) were measured and their thermoelectric figures of merit are evaluated at room temperature. All of the compounds have positive Seebeck coefficients. The lattice thermal conductivity increases linearly with the increase of the microhardness for AIBVX2 and A3 IBVX4s eries. The Keyes' relationship between lattice thermal conductivity and melting point are applicable for AIBVX2 and A3 IBVX4 series. On the other hand, the lattice thermal conductivity of A2 IBIVX3 series does not satisfy the usual relationships mentioned above. Values of zmax, the value of the thermoelectric figure of merit at the optimized carrier concentration estimated by the formulas based on the simplified assumptions are in the order of 10-5 deg-1., 10-4 deg-1. and 10-3 deg-1. for sulphides, selenides and tellurides, respectively. The value of zmax of Cu3SbTe4 is estimated to be 2.8×10-3 deg-1.