Electrical conductivity of novel tetragonal t′meta-(Ce0.5Zr0.5)O2 phase prepared by reduction and successive oxidation of t′ phase

A tetragonal t'-(Ce0.5Zr0.5)O-2, (t'), prepared from ceria and zirconia mixtures by a conventional ceramic method, was reduced at 1123 K and successively oxidized at 873 K to attain a novel tetragonal phase, t(meta)'-(Ce0.5Zr0.5)O-2 (t(meta)'). The electrical conductivity sigma(t) of t(meta)' was measured as a function of temperature and time and compared with that for t'. The conducting species were also discussed on the basis of the measurements 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 reproducible 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 that a phase transition, t(meta)' --> t', occurred above 1173 K. It was concluded 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(meta)' and t' are the predominant electronic conductors, possibly because of a hopping mechanism. (C) 2000 Academic Press.