Rhombohedral and monoclinic modifications of this compound were studied by means of X-ray diffraction, infra-red analysis, Raman light-scattering, differential thermal analysis, differential scanning calorimetry and impedance spectroscopy at temperatures ranging from 290 to 600K. An analysis of the data led to the suggestion that the super-ionic phase transition, which was observed in these materials at temperatures of between 370 and 385K, was a Faraday-type phase transformation. The PO4 tetrahedra which were part of the rigid (In2P3O12)3003- skeleton were found to be deformed. This appeared to be due to an ordered Li ion-vacancy distribution in the low-temperature non-superionic polymorphs. These deformations disappeared with increasing temperature, and the disappearance was attributed to a decrease in the correlation length of the Li ion-vacancy order.

V.V.Kravchenko, S.E.Sigaryov: Journal of Materials Science, 1994, 29[22], 6004-10