The O ion conductivity was studied in solid solutions of the form, Ca1-xNaxBi2Nb2O9-x/2, where x was between 0 and 1, and CaBi2Nb2-yTiyO9-y/2, where y was between 0 and 0.15. At an x-value of 0.1, the conductivities of Ca1-xNaxBi2Nb2O9-x/2 and CaBi2Nb2O9 were similar. On the other hand, the substitution of Ti for Nb to give the same O vacancy concentration (y = 0.1) decreased the activation energy to 1.0eV, from the value of 1.7eV in the parent compound. When x was between 0.2 and 1, all of the samples exhibited a discontinuity in the Arrhenius plots of the conductivity at 850C. Differential thermal analyses confirmed the occurrence of a phase transformation which was attributed to an order-disorder transition of the O vacancies. A change in the activation energy was also observed at lower temperatures. Measurements of the electronic conductivity, and of the effect of the O partial pressure upon the conductivity, suggested that this transition was due to a change from an ionic extrinsic regime to an ionic intrinsic regime.

A.Q.Pham, I.Yazdi, A.J.Jacobson: Journal of the Electrochemical Society, 1995, 142[5], 1559-63