Synthesis,Microstructure And Thermoelectric Properties Of Ternary Compounds In The SnTe-Bi₂Te₃ System

Bismuth telluride based alloys have been a class of important thermoelectric materials widely used in cooling devices around room temperature. Recently, there has been a rebirth of much interest in BiaTea renewed alloys. In this work, the synthesis method, sintering process, microstructure, thermoelectric properties of ternary (SnTe)x(Bi2Te3)y compounds are studied.A serials of polycrystalline samples of the ternary compounds in the (SnTe)x(Bi2Te3)y system were prepared by a rapid quenching of the melt followed by a sintering procedure of compacted pellets. The electrical conductivity and Seebeck coefficient of these samples with various compositions were measured from the room temperature up to about 600 K. The measured results show that the transport properties greatly vary with the composition and temperature, SnBi4Te7(x:y=l :2) exhibits the best power factor around 350 K, and then decreases dramatically as the temperature goes up. The microstructure in this system shows randomly oriented fine plate-shaped grains with multi-layered structure. The fine grains randomly oriented (strong grain boundary scattering) and pores in these sintered samples could decrease the electrical conductivity. However, on the other hand, the fine grains randomly oriented and pores could lead to a dramatic decrease in the thermal conductivity. The microstructure of the polycrystal remains to be optimized to achieve good performance.To reduce the high cost and high-energy expedition of melting method, a solvothermal process followed by a sintering procedure of compacted pelletsproduced by using cold isostatic pressure method were mentioned to prepare polycrystalline samples of the ternary (SnTe)x(Bi2Te3)y compounds. The samples with smaller grain sides were obtained in our experiment, and the properties are corresponding with that of those samples prepared by melting method mentioned previously. Several approaches can be proposed for further increasing the thermoelectric properties. Preparation of the material with different compositional deviations availably controlled from stoichiometry is one of the ways to change the carrier concentration, and hence to optimize the value of power factor. The thermoelectric properties can also be improved by enhancing the purity and optimizing the microstructure of this polycrystal.