The electrical conductivity of the undoped oxide was evaluated by using impedance spectroscopy. A new phenomenon was observed which was not related to the electrode response, but probably to diffusion processes in the grain boundary. An equivalent circuit was constructed, based upon this observation, and the electronic bulk, ionic grain, and ionic grain boundary conductivities were calculated. Evaluation, by fitting results to the proposed equivalent circuit, suggested that diffusion-related phenomena were caused by blocking effects in the grain boundaries; due to impurity segregation. Investigation of the grain boundary composition by using energy-dispersive X-ray spectroscopy showed that it contained detectable amounts of impurities when compared with the grain.

Impedance Studies of Diffusion Phenomena and Ionic and Electronic Conductivity of Cerium Oxide. P.Jasinski, V.Petrovsky, T.Suzuki, H.U.Anderson: Journal of the Electrochemical Society, 2005, 152[4], J27-32