Crystal structure and oxide ion conductivity of a series of Ti and Ti-Cu double substituted Bi4V2O11 compounds, Bi2V1-xTixO(11-x)/2 (0.085 ≤ x ≤ 0.15), and Bi2V0.9Cu0.1-xTixO5.35+x (0 ≤ x ≤ 0.1), were investigated by using X-ray powder diffraction and alternating-current impedance spectroscopy in the temperature and frequency range of 100–700C and 10-2–107Hz, respectively. Structural phase transitions, α → β and β → γ, occurred as a function of composition in Ti substituted compounds for which the γ was evidenced to be stable at room temperature when x exceeds 0.125. For all Ti-Cu double substituted compounds studied, the room temperature phase was identified to be γ phase. The required amount of Ti for γ phase stabilization at room temperature was significantly reduced and the conductivity improved when Cu substituted a part of Ti. Therefore, for the Bi2V0.9Cu0.1-xTixO5.35+x (0 ≤ x ≤ 0.075) compounds the ionic conductivity increased and activation energy decreased with decreasing x. At low temperature, the highest ion conductivity was obtained for Bi2V0.9Cu0.1O5.35. At high temperature (T>500C), a different behavior was observed. The total conductivity increased at first with decreasing x values down to x = 0.05 and then decreased. The maximum conductivity was obtained for Bi2V0.9Cu0.05Ti0.05O5.4, and the activation energy decreased with decreasing x values, such as what happened at low temperature.

Ionic Conductivity and Crystal Structure Relationships in Ti/Cu Substituted Bi4V2O11. M.H.Paydar, A.M.Hadian, G.Fafilek: Journal of Materials Science, 2004, 39[4], 1357-61