Effect of excess Ge and Te on thermoelectric performance of GeTe

Abstract

AbstractGeTe is a medium‐temperature thermoelectric material with excellent performance. The thermoelectric performance of GeTe is affected by the carrier concentration generated by Ge vacancy. Therefore, it is of important to study the effect of excess Ge or Te on the thermoelectric performance of GeTe. In this paper, GexTey materials (x:y = 1:1.08, 1:1.06, 1:1.04, 1:1, 1.05:1, 1.075:1, and 1.1:1) were fabricated by high‐pressure sintering (HPS) and spark plasma sintering (SPS), respectively, to study the effects of different Ge/Te atomic ratios and preparation process on the thermoelectric properties of polycrystalline GeTe. The composition and microstructure were investigated by an X‐ray diffraction method (XRD) and field‐emission scanning electron microscope (FESEM). The thermoelectric performance was tested from 303 to 703 K. The measurement results show that the Seebeck coefficient of GexTey increases and the conductivity decreases with the decreasing in Te content or the increasing in Ge content. Ge1Te1 exhibits the highest power factor because its Seebeck coefficient and conductivity are at an average level. Owing to the presence of pure Ge and the decrease of Ge vacancy, the lattice thermal conductivities of samples with excess Ge are higher than that of Ge1Te1. Ge1Te1 sintered by HPS has the highest ZTmax value, reaching 1.37 at 723 K.