Lattice thermal expansion studies of V2GeO4F2: A topaz type oxide-fluoride

A new compound V2GeO4F2 was earlier found to exist in the V2O3–VF3–GeO2 system and the structure elucidation revealed it to be iso-structural to the mineral topaz. Herein, we report the lattice thermal expansion data of this compound. The lattice thermal expansion of V2GeO4F2 was studied in the temperature range of 298–873 K under a flowing helium atmosphere by the high temperature XRD (HTXRD). The coefficients of axial thermal expansions of V2GeO4F2 were found to be as: αa = 3.5 × 10−6, αb = 6.1 × 10−6 and αc = 7.6 × 10−6 K−1. The coefficient of volume (αV) thermal expansion was 17.3 × 10−6 K−1, which is relatively low compared to many analogues silicates.