Thermal stability and electrical transport properties of Ge/Sn-codoped single crystalline β-Zn4Sb3 prepared by the Sn-flux method**Project supported by the National Natural Science Foundation of China (Grant No. 51262032).

Abstract

This study prepares a group of single crystalline β-Zn4Sb3 with Ge and Sn codoped by the Sn-flux method according to the nominal stoichiometric ratios of Zn4.4Sb3GexSn3 (x = 0–0.15). The prepared samples possess a metallic luster surface with perfect appearance and large crystal sizes. The microscopic cracks or defects are invisible in the samples from the back-scattered electron image. Except for the heavily Ge-doped sample of x = 0.15, all the samples are single phase with space group . The thermal analysis results show that the samples doped with Ge exhibit an excellent thermal stability. Compared with the polycrystalline Ge-substituted β-Zn4Sb3, the present single crystals have higher carrier mobility, and hence the electrical conductivity is improved, which reaches 7.48 ×104 S·m−1 at room temperature for the x = 0.1 sample. The change of Ge and Sn contents does not improve the Seebeck coefficient significantly. Benefiting from the increased electrical conductivity, the sample with x = 0.075 gets the highest power factor of 1.45 ×10−3 W·m−1·K−2 at 543 K.