Design of Ball-Milling Experiments on Bi2Te3 Thermoelectric Material

In this work, factorial ball-milling experiments have been applied to Bi2Te3 material, for the first time, aiming to investigate the effect of the main process parameters on the structural features and thermoelectric properties of the ball-milled materials. The selected main parameters were the duration of milling, the speed, and the ball-to-material ratio. Analysis suggests a strong effect of the speed and duration of processing, whereas the ball-to-material ratio is of minor importance. This approach is advantageous for better understanding of the milling mechanism and the importance of the role of each independent parameter as well as their interaction. All experiments led to nanocrystalline Bi2Te3, whose structural features were studied. The nanocrystalline size was estimated based on x-ray diffraction analysis, while transmission electron microscopy (TEM) studies were also performed to confirm the presence of nanoscale crystals. A mathematical model was developed based on statistical analysis for prediction of the crystalline size and the Seebeck coefficient of the nanopowders. The thermoelectric properties were also investigated on selected, highly dense pellets fabricated via hot-pressing of the nanopowders.