Abstract:The phase formation and thermoelectric (TE) properties in the central region of the Zn-Sb phase diagram were analyzed through synthesizing a series of Zn_1+xSb (x=0, 0.05, 0.1, 0.15, 0.25, 0.3) materials by reacting Zn and Sb powders below the solidus line of the Zn-Sb binary phase diagram followed by furnace cooling. In this process, the nonstoichiometric powder blend crystallized in a combination of ZnSb and β-Zn₄Sb₃ phases. Then, the materials were ground and hot pressed to form dense ZnSb/β-Zn₄Sb₃ composites. No traces of Sb and Zn elements or other phases were revealed by X-ray diffraction, high resolution transmission electron microscopy and electron energy loss spectroscopy analyses. The thermoelectric properties of all materials could be rationalized as a combination of the thermoelectric behavior of ZnSb and β-Zn₄Sb₃ phases, which were dominated by the main phase in each sample. Zn_1.3Sb composite exhibited the best thermoelectric performance. It was also found that Ge doping substantially increased the Seebeck coefficient of Zn_1.3Sb and led to significantly higher power factor, up to 1.51 mW·m^-1·K^-2 at 540 K. Overall, an exceptional and stable TE figure of merit (Z_T) of 1.17 at 650 K was obtained for Zn_1.28Ge_0.02Sb.

Key words: Zn_1+xSb; ZnSb/β-Zn₄Sb₃ composite; thermal stability; thermoelectric properties