Studies on Some Ternary Oxides of AVO3 Composition

AVO₃ (A = Ba²⁺, Sr²⁺, La³⁺, Gd³⁺) oxides have been prepared by hydrogen reduction of suitable vanadium(V) ternary oxides. The oxidation state of vanadium in the reduction products seems to be controlled by the nature of other cations. In the presence of strongly basic alkaline-earth metal ions, Ba²⁺ and Sr²⁺ as in Ba₂V₂O₇ and Sr₂V₂O₇, vanadium is reduced to +4 state. But when A is a trivalent lanthanide ion as in LnVO₄ (Ln = La or Gd), the reduction of vanadium proceeds to +3 state to yield LnVO₃ phases. The products have been characterized by X-ray diffraction. BaVO₃ crystallizes in a hexagonal structure related to Ba₃V₂O₈ while SrVO₃, LaVO₃ and GdVO₃ crystallize in GdFeO₃ type structure. Electrical transport measurements indicate that BaVO₃, LaVO₃ and GdVO₃ are p-type semiconductors while SrVO₃ is metallic.