Structure and microstructure of In4Te3 nanopowders prepared by solid state reaction

In this paper, we investigated the structure and microstructure of In4Te3 nanopowders obtained by mechanically alloying an In75Te25 powder mixture. Structural, chemical, thermal and vibrational studies of the In75Te25 powder mixture were carried out using X-ray diffraction, energy dispersive spectroscopy, transmission electron microscopy, differential scanning calorimetry and Raman spectroscopy. The orthorhombic In4Te3 phase (In3Se4-type) was nucleated in 2 h of synthesis, although non-reacted tetragonal indium (In) was still present at that time. Small amounts of cubic In2O3 phase were observed after 31 h of synthesis. Rietveld analyses allowed the measurement of mean crystallites sizes and phase fraction variations when milling times were increased. These analyses showed that, after 31 h of synthesis, about 65 wt% of In4Te3 phase contained mean crystallite sizes smaller than 27 nm and microstrains greater than 1.5%. The crystallite and interfacial components sizes were determined by high resolution transmission electron microscopy. Differential scanning calorimetry measurements showed the influence of nanometric crystallite sizes on the melting of the In4Te3 and non-reacted In phases. Raman measurements showed that the trigonal Te and α-TeO2 modes, observed for the precursor Te powder, are absent for the sample milled for 31 h. The structural stability of the nanocrystalline phases of the In75Te25 sample milled for 31 h was attested by X-ray diffraction measurements performed twelve months after its production.