Thermoelectric properties of GeTe-based composites prepared by spark plasma sintering containing Bi/Sb additive

Spark plasma sintering (SPS) is often used to prepare bulk thermoelectric (TE) materials, and the application of additives during the process may have a unique effect on constructing multiphase structures. The additives with low melting points can be often extruded or react with the matrix during the SPS process, leaving dense dislocations or multiphase structures to optimize the TE performance. In this paper, high-performance GeTe-based composites were prepared by SPS containing Bi or Sb additive. During the SPS process (sintering temperature 773 K), the Bi (melting point 544 K) or Sb ( 904 K) additive have the liquid-solid/solid-solid reaction with the GeTe matrix, respectively. The chemical reactions lead to the composite structures of the matrix and pseudobinary alloy (GeTe)x(Bi2Te3) or (GeTe)y(Sb2Te3) with 7 <= (x, y) <= 9, resulting in a significant increase in the Seebeck coefficient by the energy filtering effect and the reduction of thermal conductivity by enhancing the phonons scattering. The influence of the Sb additive is better than that of Bi, therefore, the sample with 1 wt% Sb has a ZTmax value of 1.49 at 685 K, 157 % higher than that of the matrix (0.58). This study shows that SPS with appropriate additives is an effective method to prepare high-performance GeTe-based TE composites.