Thermal and microstructure simulation of thermoelectric material Bi sub(2)Te sub(3) grown by zone-melting technique

The thermoelectric conversion efficiency of the thermoelectric material Bi sub(2)Te sub(3) is significantly affected by its microstructure because of its anisotropy. In this study, the zone-melting technique is used to grow Bi sub(2)Te sub(3) columnar crystals. The zone-melting process directionally solidifies and purifies an ingot by a moving a heater along the ingot. For predicting the temperature variation and distribution in the crystallization process and the microstructures of Bi sub(2)Te sub(3), a zone-melting model is developed and numerical simulation techniques are used. The simulation results are compared with experimental measurements to verify the numerical model. The verified numerical model is used to investigate the optimal process parameters. The process parameters, namely the temperature of the heater and the movement speed of the heater and the cooling devices, are adjusted in order to obtain good-quality columnar crystals. The shapes of the solidification interface, which greatly affect the direction of grain growth and the grain size, are compared.