Thermal stability and electrical transport properties of Ge/Sn-codoped single crystalline β-Zn_4Sb_3 prepared by the Sn-flux method

This study prepares a group of single crystalline β-Zn_4Sb_3 with Ge and Sn codoped by the Sn-flux method according to the nominal stoichiometric ratios of Zn_（4.4）Sb_3 Ge_xSn_3（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 R3c. The thermal analysis results show that the samples doped with Ge exhibit an excellent thermal stability.Compared with the polycrystalline Ge-substituted β-Zn_4Sb_3, the present single crystals have higher carrier mobility, and hence the electrical conductivity is improved, which reaches 7.48×10~4S·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.