Phase formation and thermoelectric properties of Zn1+Sb binary system

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 Zn1+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. Zn1.3Sb composite exhibited the best thermoelectric performance. It was also found that Ge doping substantially increased the Seebeck coefficient of Zn1.3Sb 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 (ZT) of 1.17 at 650 K was obtained for Zn1.28Ge0.02Sb.