A new phase Cu₂V₂O₇ synthesized, exhibits phase transitions between 475°C and 500°C. These phase transitions are reversible with ease in contrast toα →β phase transition at 712°C of Cu₂V₂O₇ phase reported earlier. These phase transitions are identified by DTA technique and characterized by detailed XRD investigations at different temperatures. The crystal structures of these Cu₂V₂O₇ phases are related to either thortveitite (Sc₂Si₂O₇) type or a modification of it.

Data on the polymorphs of copper(II) orthovanadate are reported. The Cu₃V₂O₈ phase synthesized in this laboratory exhibits phase transitions between 460° and 560°C. These phase transitions are identified through detailed DTA and high temperature XRD techniques; it is observed that these structural transitions are rapid and reversible. The crystal structure of Cu₃V₂O₈ is similar to that of Mg₃V₂O₈, Zn₃V₂O₈, Co₃V₂O₈ and Ni₃V₂O₈.

Iron(III) vanadate (FeVO₄) is an n-type semiconductor between 300 and 800 K. Electrical conduction in this phase occurs due to small deviation from oxygen stoichiometric composition. The mechanism of electrical transport is of a thermally activated hopping of charge carriers (electrons) on equivalent iron lattice sites. The FeVO₄ obeys Curie-Weiss law between 80 and 300 K. The measured magnetic moment (μ_eff) of Fe³⁺ ion in FeVO₄ is 5·270 BM at 298 K, which is lower than theμ_spin only value. The predominant exchange interactions are the weak 90° M-O-M superexchange and M-O-O-M super-super-exchange. The negative Weiss constantϑ=− 30 K of the phase indicated the possibility of an antiferromagnetic ordering of the iron(III) vanadate lattice. The IR absorption spectrum of FeVO₄ gave bands at 990, 900, 825 and 725 cm⁻¹ due to the presence of distorted VO₄ polyhedra of the lattice.

Cerium(III) orthovanadate with a small deviation from stoichiometric composition is ap-type semiconductor between 30 and 800°C. The electrical conduction in cerium(III) orthovanadate is due to thermally activated hopping of holes on equivalent Ce³⁺-Ce⁴⁺ lattice sites. The DTA result of CeVO₄ indicated a possible phase transition at about 70°C. The IR spectrum of the sample showed bands at 865 and 810 cm⁻¹, typical of VO₄ group of orthovanadates.

Cadmium(II) metavanadate has crystal structure related to brannerite (ThTi₂O₆) structure. The high temperatureβ-CdV₂O₆ phase isn-type semiconductor between 185 and 750°C. The electrical conduction in theβ-CdV₂O₆ occurs due to deviation from oxygen stoichiometric composition of the lattice. The seebeck coefficient (α) of the sample is negative and constant in the entire range of investigation. The mechanism of transport in cadmium metavanadate lattice is via thermally activated hopping of localized electrons on vanadium (V⁵⁺) sites of the lattice. The DTA result indicated that CdV₂O₆ undergoes phase transition at 185°C and not at 670°C as reported earlier. There is no DTA evidence to show the possibility ofβ →α phase reverse transition. The XRD powder patterns of the two modifications are nearly similar indicating brannerite related structures. The infrared absorption band of vanadium-oxygen stretching vibration modes of distorted VO₆ octahedra ofβ-CdV₂O₆ is exhibited at 855 cm⁻¹.