Preparation and Thermoelectric Transport of Polycrystalline In4Se3 with High Figures of Merit

Polycrystalline In4Se3 thermoelectric materials were synthesized in the processing sequence of vacuum melting, annealing and spark plasma sintering. The effect(s) of melting and annealing duration periods on the phase, composition, microstructure, and thermoelectric properties of polycrystalline In4Se3 were investigated. After the melting process, both In and InSe phase were detected in the ingots. With increasing melting duration time, an increase in Se deficiency was observed, leading to an increase of carrier concentration, which contributed to the observed improvement of electrical conductivity. The specimen melted for 48 h showed relatively higher ZT. Thus on the basis of 48 h melting process, the ingots were then annealed for different periods of time, which eliminated the presence of InSe phase. After annealing, scattered large step-like structures were observed in the matrix, which favored the reduction of thermal conductivity but had no significant influence on the electrical conductivity. The ZT was significantly enhanced to 0.83 at 702 K by extending melting and annealing duration time to 48 h and 96 h, respectively, which is 32% higher than that reported in literature. It was concluded that both the extension of melting and annealing duration periods could improve the thermoelectric performance of polycrystalline In4Se3.