Enhanced Thermoelectric Properties Obtained by Compositional Optimization in p-Type Bi x Sb2−x Te3 Fabricated by Mechanical Alloying and Spark Plasma Sintering

Abstract

BixSb2−xTe3 bulk alloys are known as the best p-type thermoelectric materials near room temperature. In this work, single-phase BixSb2−xTe3 (x = 0.2, 0.25, 0.3, 0.34, 0.38, 0.42, 0.46, and 0.5) alloys were prepared by spark plasma sintering (SPS) using mechanical alloying (MA)-derived powders. A small amount (0.1 vol.%) of SiC nanoparticles was added to improve the mechanical properties and to reduce the thermal conductivity of the alloys. The electrical resistivity decreases significantly with increasing ratio of Sb to Bi in spite of the weaker decreasing trend in Seebeck coefficient, whereby the power factor at 323 K reaches 3.14 × 10−3 W/mK2 for a sample with x = 0.3, obviously higher than that at x = 0.5 (2.27 × 10−3 W/mK2), a composition commonly used for ingots. Higher thermal conductivities at low temperatures are obtained at the compositions with lower x values, but they tend to decrease with temperature. As a result, higher ZT values are obtained for Bi0.3Sb1.7Te3, with a maximum ZT value of 1.23 at 423 K, about twice the ZT value (about 0.6) of Bi0.5Sb1.5Te3 at the same temperature.