Amorphization of Ca3(VO4)2 at high pressure

The combined X-ray diffraction and Raman spectroscopy data show that Ca3(VO4)2 irreversibly amorphizes at 10.0 GPa and room temperature. The amorphization, with its onset at about 8.5 GPa, is not preceded by any phase transition in the crystalline phase, which possesses highly anisotropic compressibility (the axial stiffness along the a axis is over 30% larger than the axial stiffness along the c axis). The results of Raman spectroscopy measurements demonstrate that structural rearrangements in the amorphous Ca3 (VO4)2 occur between 8.1 and 14.8 GPa. This is associated with a large deformation of the VO43- units or the increase of the average coordination number for the V5+ cations in the amorphous material. A large hysteresis of this phase change is observed upon decompression, suggesting a first-order character of polymorphic transitions within the amorphous material