Structural and electrical behavior of Bi2VO5 with temperature.: Stabilization at room temperature of the high temperature polymorphs

Mixed bismuth(III)–vanadium(IV) oxide Bi2VO5 was prepared as a very crystalline powder by solid-state reaction under vacuum and N2 flow. Thermal analysis and powder X-ray diffraction at high temperatures confirmed the existence of two phase transitions, α → β at 397°C and β → γ at 778°C due to the progressive loss of oxygen vacancy ordering. Impedance spectroscopy measurements showed that this material is a good ionic conductor. This is particularly true of the β-phase, which exhibits a conductivity as high as 5 × 10–2Ω–1·cm–1 at 700°C. Three solid solutions Bi2V1–xGexO5 (0 ≤ x < 0.5), Bi2V1–yTiyO5 (0 ≤ y ≤ 0.1) and Bi2V1–zFezO5–z/2 (0 ≤ z ≤ 0.4) were studied. The X-ray powder diffraction patterns show that partial substitution of isovalent Ge(IV) and Ti(IV) or aliovalent Fe(III) on the V(IV) site stabilizes the high-temperature β-phase (x < 0.5, z ≤ 0.4) and γ-polymorph (y ≤ 0.1).