  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.
