Structural phase transition in indium tungstate

Abstract

Structural phase transition in ${\mathrm{In}}_2{\mathrm{W}}_3{\mathrm{O}}_{12}$ has been studied using differential scanning calorimetry, dilatometry, and Raman spectroscopy. The phase transition at 523 K has been found to be of first order with a heat of transition of 1.22 kJ/mole. In contrast to the earlier reports, the present dilatometric studies suggest that high temperature phase could have a small positive thermal expansion. Phonon frequencies in the monoclinic phase of this network structure were obtained from the Raman spectrum at 10 K. Large discontinuous changes in phonon frequencies are not found across the phase transition; however, temperature coefficients of phonon frequencies exhibit changes. Present results indicate that the local environment of tungstate ions in the high temperature phase is not significantly different from that in the monoclinic phase. Furthermore, weak temperature dependence of the phonon frequencies suggests that their anharmonicities are small in the high temperature phase and this could be responsible for the low value of thermal expansion.