The impedance of these ceramics was measured at frequencies ranging from 5Hz to 10MHz, and temperatures of between 410 and 980K. The conductivity of the samples was deduced from a non-linear least-squares analysis of the impedance spectra. A change in the slope of Arrhenius plots of the total conductivity was found for both materials. Transition temperatures which were detected by means of differential thermal analysis coincided with those which were observed in conductivity data, and were attributed to a phase transition that involved re-ordering of the O ions.

P.Kurek, M.W.Breiter: Solid State Ionics, 1996, 86-88[1], 131-5