High-pressure powder diffraction study of TaO2F

TaO2F, with a ReO3-type structure, has been studied at up to 12.8 GPa using monochromatic synchrotron powder diffraction and diamond anvil cells. Two-phase transitions at ∼0.7 and 4 GPa were observed on compression. Below ∼0.7 GPa the cubic material was found to have a bulk modulus (K0) of 36(3) GPa (Kp fixed at 4.0), similar to that reported for NbO2F but much smaller than that of ReO3. Immediately above 0.7 GPa on compression, the diffraction data were not fully consistent with a VF3-type structure as previously proposed for NbO2F. On decompression, the data between 8 and 4 GPa could be satisfactorily attributed to a single R-3c phase with a VF3-type structure and an average bulk modulus of 60(2) GPa.