Microstructural Engineering And Thermoelectric Properties Of Pseudo-Binary Sn-Bi-Te Systems)

Abstract

The growing demand for energy needs better materials for energy conversion. One class of materials to address the problem are materials for conversion of waste heat to electricity, which are called thermoelectric materials. Even though SnTe and Bi2Te3 are important thermoelectric materials, the phase diagram and microstructural studies of their pseudo-binary system are not well investigated. Since these microstructures can determine the property of the material, investigation of the relationship between microstructure and thermoelectric property of Sn-Bi-Te system is anticipated to result in the finding of new thermoelectric material. Therefore, this research is aimed to study the variation of microstructures with the composition of selected samples. The thermoelectric properties have been investigated as a function of variation in microstructures. This research contains two parts. The first part aims at determining the effect of Bi addition to the SnTe system. It includes investigation of the microstructural, mechanical and thermoelectric properties of the system. This work describes the nature of the microstructure of the system. The study of the mechanical property concerns the change of Vickers hardness with aging heat treatment. The study of the thermoelectric properties was as a function of both composition and temperature. This group samples had created small SnTe phases compacted with Bi. Such a structure has a high probability of scattering phonon while allowing electrical conduction and hence enables the high value of the Seebeck coefficient. The second part considers a group of samples which were studied to investigate the relatively complex nature microstructure of the SnTe - Bi2Te3 system. It focuses on the region where Bi2Te3 is soluble in SnTe. Both composition and processing methods result in the creation of different kind of microstructures. The study of the microstructure in this region focuses on determining the phases and crystal structure of the system. This part of the research aims at exploring different compositions which have a high potential for thermoelectric application.