Ionic conductivity and crystal structure relationships in Ti/Cu substituted Bi4V2O11

Crystal structure and oxide ion conductivity of a series of Ti and Ti-Cu double substituted Bi4V2O11 compounds, Bi2V(1−x)Ti x O(11−x)/2 (0.085 ≤ x ≤ 0.15), and Bi2V0.9Cu(0.1−x)TixO5.35+x (0 ≤ x ≤ 0.1), were investigated using X-ray powder diffraction and ac impedance spectroscopy in the temperature and frequency range of 100–700°C and 10−2–107 Hz, respectively. Structural phase transitions, α → β and β → γ, occur as a function of composition in Ti substituted compounds for which the γ is 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 Bi2V0.9Cu(0.1−x)Ti x O5.35+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>500°C), 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.