Phase transformation in early stage formation of thermoelectric nanocrystalline Bi₂Te₃ synthesized by mechanical alloying

Nanocrystalline bismuth telluride, Bi₂Te₃ has been synthesized by mechanical alloying the stoichiometric powder mixture of elemental Bi and Te at room temperature under Ar within a very short duration of milling. Microstructure characterization of as milled powders has been carried out employing Rietveld powder structure refinement method using X-Ray powder diffraction (XRD) data. XRD pattern of 15 min milled powder is composed of major Bi₂Te₃ phase with other two minor phases. Here, we report detailed structure information of these minor phases which were not focused in previous works. XRD analysis reveals that stoichiometric Bi₂Te₃ phase has been formed after 1h of milling and there is no phase transition up to 10h of milling. The crystallite size and lattice strain values of Bi₂Te₃ are found as anisotropic. Microstructure characterization of 10 h milled powder by HRTEM also reveals the formation of single phase nanostructured Bi₂Te₃ with size anisotropy. (author)