Mixed bismuth(III)-vanadium(IV) oxide Bi 2 VO 5 was prepared as a very crystalline powder by solid-state reaction under vacuum and N 2 flow. Thermal analysis and powder X-ray diffraction at high temperatures confirmed the existence of two phase transitions, α -> β at 397 o C and β -> γ at 778 o 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 x 10 - 2 Ω - 1 .cm - 1 at 700 o C. Three solid solutions Bi 2 V 1 - x Ge x O 5 (0 =< x < 0.5), Bi 2 V 1 - y Ti y O 5 (0 =< y =< 0.1) and Bi 2 V 1 - z Fe z O 5 - 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).