On the Mechanism of Thermal Expansion of Orthorhombically Modified Copper Pyrovanadate

A set of X-ray diffraction data on the crystal-lattice transformations of the α-Cu 2 V 2 O 7 phase demonstrates that, in regions with an anomalous negative and near-zero volumetric thermal expansion, both vanadium‒oxygen and copper‒oxygen sublattices are maximally deformed. The near-zero and negative volumetric thermal expansion of the α-Cu 2 V 2 O 7 unit cell arises from the degeneration of zigzag copper‒oxygen columns at invariable distances between Cu–O sublattice layers.