Variations in the extent of pyrochlore-type cation ordering in Ce2Zr2O8: A t' - k pathway to low temperature reduction.

A Ce2Zr2O8 mixed oxide was prepared, and the influence of redox treatments on its reduction behaviour was analyzed. The temperature of reduction was found to change on application of redox cycles under severe conditions, with the final appearance of temperature-programmed reduction profiles dictated by the exact conditions employed (temperature and H2 concentration). The reduction was found to vary from a single high-temperature peak to a single low-temperature peak, via various double-peak profiles. Structural analysis of the sample indicated that the reduction behaviour follows a pathway, with t′ and κ phases at the two extremes. The latter phase contains pyrochlore-type cation ordering. However, bulk ordering is not necessary to promote low-temperature reduction. The evidence suggests that the two-peak profiles are observed when cation ordering is very limited, and a single low-temperature peak is observed when domains of the κ phase coexist with larger amounts of the t′ phase.