Thermoelectric properties of vacuum melted Zn4−xCoxSb3 compounds

The effect of Co substitution for Zn on the thermoelectric properties of beta-Zn₄Sb₃ was investigated to optimize the relatively low electrical conductivity and Seebeck coefficient. Zn_4-xCo_xSb₃ compounds with times=0.1~0.5 were prepared by vacuum melting the metal elements at 1173 K in quartz tube and subsequent homogenization annealing of air cooled ingots at 673 K. Microstructures analyzed by XRD and variation of thermoelectric properties with amounts of Co substitution showed that Co substitution over times=0.3 resulted in the formation of CoSb₃ phase. Seebeck coefficient and electrical resistivity of Co substituted Zn₄Sb₃ increased with increasing temperature, showing metallic conduction. As Co substitution amounts increased, both electrical resistivity and Seebeck coefficient decreased, reached minimum value around times=0.3, and then increased. But thermal conductivity increased with increasing substituted Co. This behavior of thermoelectric properties is believed to be resulted from the formation of CoSb₃ phase over times=0.3.