Thermal and microstructure simulation of thermoelectric material Bi2Te3 grown by zone-melting technique

• Published in: Journal of crystal growth 2014-09, Vol.402, p.273-284
• Main Authors: Chen, Yi-Ru, Hwang, Weng-Sing, Hsieh, Huey-Lin, Huang, Jing-Yi, Huang, Tsai-Kun, Hwang, Jenn-Dong
• Format: Article
• Language: English
• Subjects: A1. Solidification; Bi2Te3; Cellular automaton (CA) method; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Directional growth; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; Growth from melts; zone melting and refining; Materials science; Methods of crystal growth; physics of crystal growth; Numerical simulation; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Physics; Solid-solid transitions; Solidification; Specific phase transitions; Theory and models of crystal growth; physics of crystal growth, crystal morphology and orientation; Thermoelectric materials; Zone-melting technique
• ISSN: 0022-0248; 1873-5002
• DOI: 10.1016/j.jcrysgro.2014.05.023

The thermoelectric conversion efficiency of the thermoelectric material Bi2Te3 is significantly affected by its microstructure because of its anisotropy. In this study, the zone-melting technique is used to grow Bi2Te3 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 Bi2Te3, 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. •A numerical model has been established and has been validated by experimental measurements.•The model is used to study the effects of process conditions on the microstructure; grain size..•The largest grain size is 6.9 mm, with heater temperature of 770 °C, heater speed of 0.75 cm/hr.•The shape of solidification interface has a great impact on growth direction and size of grain.