Thermoelectric properties of intermetallic compounds: Mg3Bi2 and Mg3Sb2 for medium temperature range thermoelectric elements

Hot-press sintered thermoelectric elements of intermetallic compounds: Mg₃Bi₂ and Mg₃Sb₂ were examined for the feasibility as medium temperature range thermoelectric elements, which belong to the family of zinc blend crystal structure. The experiments were carried out varying the sintering temperature in order to find out the optimum morphology for the sintered material system, because the thermoelectric performance was affected with the macro- and micro-structure due to the sintering, process. Seebeck coefficients (S), electrical conductivity (σ) and thermal conductivity (κ) were measured in the temperature range from 300K to 773K. According to the Seebeck coefficient measurement, both materials were p-type semiconductor. As the results, the power factor (=S²σ) could be obtained from 1.0x10^-3 W/m²K at 550K to 2.5x10^-3 W/m²K at 773K for Mg₃Bi₂ system and from 1.0x10^-3 W/m²K at 600K to 2.0x 10^-3 W/m²K at 740K for Mg₃Sb₂ system respectively. The measurement of thermal conductivity by laser flash method showed that the hot-press sintered Mg₃Sb₂ element had the relatively low thermal conductivity. The estimate for Mg₃Sb₂ elements promisingly shows the dimensionless figure of merit ZT of 0.55 at 660K.