Comparative study of the high-pressure behavior of ZnV2O6, Zn2V2O7, and Zn3V2O8

We report a study of the high-pressure structural behavior of ZnV2O6, Zn2V2O7, and Zn3V2O8, which has been explored by means of synchrotron powder x-ray diffraction. We found that ZnV2O6 and Zn3V2O8 remain in the ambient-pressure structure up to 15 GPa. In contrast, in the same pressure range, Zn2V2O7 undergoes three phase transitions at 0.7, 3.0, and 10.8 GPa, respectively. Possible crystal structures for the first and second high-pressure phases are proposed. Reasons for the distinctive behavior of Zn2V2O7 are discussed. The compressibility of the different polymorphs has been determined. The response to pressure is found to be anisotropic in all the considered compounds and the room-temperature equations of state have been determined. The bulk moduli of ZnV2O6 (129(2) GPa) and Zn3V2O8 (120(2) GPa) are consistent with a structural framework composed of compressible ZnO6 octahedra and uncompressible VO4 tetrahedra. In contrast, Zn2V2O7 is highly compressible with a bulk modulus of 58(9) GPa, which is almost half of the bulk modulus of the other two vanadates. The large compressibility of Zn2V2O7 and its sequence of structural transitions are related to the fact that this material is less dense than the other zinc vanadates and to the penta-coordination of Zn atoms by oxygen atoms in Zn2V2O7. A comparison to the high-pressure behavior of related compounds is presented.