Optimum sintering method and temperature for cold compact Bismuth Telluride pellets for thermoelectric applications

Abstract

This work intends to investigate the optimum sintering method and temperature that can improve the efficiency of bismuth telluride cold compact pellets for thermoelectric applications. Different p-type and n-type bismuth telluride cold compact pellets were treated using three different sintering techniques and conditions: pressure less (conventional), microwave, and tube (using argon environment) at temperatures 250°C, 300°C, 350°C, and 400°C. The structural, microscopic, electron transport, thermal, and dielectric properties of the pristine and sintered samples were examined. Broadband dielectric spectroscopy was performed to extract a detailed picture of the dielectric properties of the samples. Even though each type of sintering had its own merits and demerits, the optimum conditions for enhanced electric and thermal features were found in microwave furnaces followed by tube and conventional. Low thermal conductivity of 0.4 W/m/K was observed in the samples sintered at 250 °C while the increase in sintering temperature from 250°C to 300°C improved the crystallinity of the material. Moreover, the crystal structure of the bismuth telluride altered with the occurrence of higher oxidation leading to the formation of high bismuth telluride oxide phases at sintering temperatures above 300°C, more dominantly in the n-type samples.