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.