Mechanical and Thermoelectric Properties of Eutectic Composite (Bi, Sb)2Te3/Te Thermoelectric Material

Abstract

Microstructural length scale of an eutectic alloy can be tuned with different cooling rates obtainable via different processing routes, such as melt spinning, suction casting and gas atomization. In this report, the thermoelectric and mechanical properties of selenium-free n-type BiSbTe compound were investigated. One kilogram of powder with a nominal composition of Bi22.5Sb7.5Te70 was fabricated using gas atomization. The powders were consolidated into a pellet using spark plasma sintering to minimize rapid grain growth, and the morphologies were examined using scanning electron microscope and X-ray diffraction techniques. The microstructure of the pellet reveals a random eutectic plate-like morphology between the primary phase and Te. The presence of Te results in excess charge carrier injection leading to a high electrical conductivity, while the reduction in length scale in the atomized samples has contributed to the decrease in the mobility of the charge carriers leading to a reasonably good Seebeck coefficient. This microstructure feature is also responsible for the high room temperature micro-Vickers hardness and a 40% reduction in the thermal conductivity. The observed thermoelectric and mechanical properties in this gas atomization + spark plasma sintering have been compared to an earlier reported processing route of flame melting. The relationship between the observed properties and microstructure features is discussed in detail.