Nanocrystalline bismuth telluride, Bi2Te3 has been synthesized by mechanical alloying (MA) the powder mixture composed of Bi and Te in the inert gas atmosphere within a short duration of 15 min. Microstructure characterization of the prepared powder has been investigated adopting the Rietveld’s method using X-Ray diffraction (XRD) data and analyzing high-resolution transmission electron microscopy (HRTEM) images. The XRD pattern of 15 min milled powder is composed of reflections of major Bi2Te3 phase with other two minor phases. Detailed structural information of these minor phases has been reported here which was not explored in any previous works. XRD analysis reveals that the stoichiometric Bi2Te3 phase has been formed after 1h of milling and there is no phase transition up to 10h of milling. HRTEM study also reveals the formation of single phase nanostructured Bi2Te3 phase. The DC (direct current) conductivities of 15min, 30min and 10h ball milled powders are measured within the temperature range of 359 to 633K. The electrical conductivity (σ) of Bi2Te3 indicates the semiconducting nature of the sample. There is no significant change of electrical conductivity of Bi2Te3 phase since its formation after 15min to 10h of milling, as there is no noticeable change in crystallite size.

Zn-ferrite nanoparticles were synthesized at room temperature by mechanical alloying the stoichiometric (1:1 mol%) mixture of ZnO and α-Fe2O3 powder under open air. Formation of both normal and inverse spinel ferrite phases was noticed after 30 minutes and 2.5 hours ball milling respectively and the content of inverse spinel phase increased with increasing milling time. The phase transformation kinetics towards formation of ferrite phases and microstructure characterization of ball milled ZnFe2O4 phases was primarily investigated by X-ray powder diffraction pattern analysis. The relative phase abundances of different phases, crystallite size, r.m.s. strain, lattice parameter change etc. were estimated from the Rietveld powder structure refinement analysis of XRD data. Positron annihilation lifetime spectra of all ball milled samples were deconvoluted with three lifetime parameters and their variation with milling time duration was explained with microstructural changes and formation of different phases with increase of milling time duration.