Preparation of nano-sized Bi2Te3 thermoelectric material powders by cryogenic grinding

A novel method for rapid preparation of Bi2Te3 nano-sized powders with an average particle size of about 70 nm was developed. A starting powder mixture consisting of Bi2Te3 coarse particles of ～5 mm was ground using cryogenic grinding in the liquid nitrogen. For comparison, the conventional high-energy ball milling was used to prepare the Bi2Te3 nano-sized powders. Sintering properties of as-prepared powders was investigated by spark plasma sintering (SPS). The effects of the preparation procedure on the crystallinity, morphology and structure were examined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). It was found that Bi2Te3 was not transformed into a non-equilibrium amorphous phase or decomposed during the cryogenic grinding process, and as-prepared nano-powders possessed excellent sinterability. This technique might also be applicable to other thermoelectric materials.