Microstructure design in Bi-Ga-Te system using a combination of thermodynamic calculations and experiments for potential thermoelectric material

Abstract

Tellurium-based alloys are emerging as attractive candidates for designing new thermoelectric materials. Various phases (e.g., Bi2Te3 and Ga2Te3) in the Bi-Ga-Te system exhibit good thermoelectric behavior. Microstructural features especially phase chemistry and fraction in alloy play a critical role in improving thermoelectric properties like the Seebeck coefficient and thermal conductivity. Although pure stoichiometric phases in Bi–Te and Ga–Te systems such as Bi2Te3 and Ga2Te3 are well investigated in the literature, there is limited study on the microstructure design in the ternary Bi-Ga-Te system that will be best suited for thermoelectric behavior. Accordingly, various alloys were developed using the recently developed thermodynamic database of the Bi-Ga-Te system. Alloys were melted in a vacuum induction furnace followed by microstructure characterization. The thermodynamic calculations and microstructural investigations of the selected compositions reveal varying phase fractions of Bi, β, Bi2Te3, Ga2Te3 and Te as both primary and eutectic phase. In addition, differential thermal analysis (DTA) was used to ascertain the phase transitions in alloys, which will assist in determining their thermoelectric operational temperature.