Effects of ageing on defect structure in the Bi3NbO7-Bi3YO6 system

Ageing effects in the defect fluorite structure of Bi3Nb1−xYxO7−x have been studied using powder neutron diffraction. Two compositions at x = 0.4 and x = 0.6 were studied after annealing for prolonged times (400-500 h) at 410 and 550 °C. The results show that significant changes in oxide ion distribution occur at 550 °C, but that at 410 °C only the lower x-value composition exhibited such a change. A comparison of lattice parameter variation with temperature for annealed and unannealed samples suggests that at higher temperatures the oxide ion distribution is independent of thermal history.