Mechanism of thermal expansion of structural modifications of zinc pyrovanadate

Crystal chemical characteristics of the α and β modifications of Zn2V2O7 are calculated based on in situ high-temperature X-ray measurements. The expansion of the structure is found to be strongly anisotropic up to the negative volumetric thermal expansion of the α-Zn2V2O7 unit cell in the temperature range of 300–600°С, α V =–17.94 × 10–6 1/K. The transformations of the “hard” and “soft” sublattices with an increase temperature and at the phase transition are considered in detail. It is shown that the negative volumetric thermal expansion of α-Zn2V2O7 is due to the degeneracy of the zigzag-like shape of zinc–oxygen columns at constant distances between their vertices.