Structural and Thermoelectric Properties of Solid-Liquid In4Se3-In Composite

The aim of our work was to investigate thermoelectric properties of a composite of solid In4Se3 and solid or liquid indium. Polycrystalline In4Se3-In composites were prepared by a direct reaction of elements, powdering of products and sintering powders by pulsed electric current sintering technique. Microstructural and structural properties of obtained composites were analyzed using SEM+EDX and XRD techniques. Electrical transport properties and thermal conductivity were measured over a temperature range of 323K <= T <= 673K. Results show that the electrical conductivity of composite increases about four times in comparison with that of pristine In4Se3. The thermal conductivity decreases in a systematic way with the increase of In content and reaches a value of about 0.44Wm(-1)K(-1). As a result, the addition of indium enhances the thermoelectric figure of merit ZT from 0.8 to 1.2 at 673K. However, we found that the melting of indium at about 430K has no significant influence on thermoelectric properties of composites. We assume that the improvement of electrical properties is mainly due to the formation of point defects in In4Se3 phase and metallic properties of the In phase. To analyze formation energies of possible defects in In4Se3 structure, DFT calculations within the molecular cluster model were carried out. It was found that the In interstitial atoms are energetically more favorable than the formation of Se vacancy in In4Se3 structure.