The δ→ε→γ LiV2O5 “High Temperature” Phase Transitions Evidenced by Synchrotron X-Ray Powder Diffraction Analysis

Abstract

The structural evolution and the temperature ranges of stability for the δ, ε, and γ phases of the lithium vanadium oxide bronze LiV2O5 are evidenced by use of synchrotron X-ray powder diffraction in the temperature range 100–250°C. It is shown that δ-LiV2O5 is stable below 120°C and that the complete transformation to the high temperature form γ-LiV2O5 is achieved above 220°C. In the temperature range 120–220°C ε-LiV2O5 is the stable polymorph. The temperature dependence of the cell parameters for the phase δ- and γ-LiV2O5 are measured and the crystal structure of ε-LiV2O5 has been determined using the Rietveld method. It crystallizes in the orthorhombic system and at 140°C the cell parameters are a=11.3552(6) Å, b=3.5732(2) Å, and c=4.6548(3) Å. Arguments supporting the choice of the space group Pmmn, as for another bronze α′ NaV2O5, are given.