Electrical conductivity of novel tetragonal t '(meta)-(Ce0.5Zr0.5)O-2 phase prepared by reduction and successive oxidation of t ' phase

A tetragonal t'-(Ce0.5Zr0.5)O-2, (t'), prepared from ceria and zirconia mix tures by a conventional ceramic method, was reduced at 1123 K and successiv ely oxidized at 873 K to attain a novel tetragonal phase, t(meta)'-(Ce0.5Zr 0.5)O-2 (t(meta)'). The electrical conductivity sigma(t) of t(meta)' was me asured as a function of temperature and time and compared with that for t'. The conducting species were also discussed on the basis of the measurement s for ionic transference number (t) over bar(ion). The sigma(t) for t(meta) ' was approximately an order of magnitude higher than that for t', and repr oducible as a function of temperature between 973 and 1073 K. At increasing temperatures above 1173 K, the sigma(t) decreased gradually with time and became consistent with t'. The change in sigma(t) resulted from the fact th at a phase transition, t(meta)' --> t', occurred above 1173 K. It was concl uded that t(meta)' is a metastable phase with lower thermodynamic stability than that of t'; however, it is virtually stable up to around 1143 K. t(me ta)' and t' are the predominant electronic conductors, possibly because of a hopping mechanism. (C) 2000 Academic Press.