Phase formation in the V2O5-Nb2O5-MoO3 system

The solid-phase interaction in the V₂O₅-Nb₂O₅-MoO₃ system has been investigated, and the formation of a solid solution bounded by the compositions MoNb₂V₄O_{18 ? δ}, Mo₂NbV₅O_{21 ? δ}, Mo₂Nb₃V₃O_{21 ? δ}, and Mo₄Nb₉V₉O_{57 ? δ} has been found (δ is nonstoichiometry). In the V₂O₅?Nb₂O₅ system, the formation of three compounds is verified, namely, VNbO₅ (tetragonal structure), VNb₉O₂₅, and V₂Nb₂₃O_62.5. The first two compounds are isostructural and form a continuous solid solution with tetragonal symmetry. A new compound of the composition Mo₃NbVO_{14 ? δ} has been synthesized. This compound is isostructural to the Mo₃Nb₂O₁₄ compound described in the literature and forms a tetragonal solid solution with it. The phase equilibria in the V₂O₅-Nb₂O₅-MoO₃ system in the subsolidus region have been determined.