Oxygen release behavior of metastable tetragonal t′meta-(Ce0.5Zr0.5)O2 phases prepared by reduction and successive oxidation of t′ phase

Tetragonal CaF2-related-type t'-(Ce0 5Zr0.5)O-2 phase was reduced at 773 K <= T-red <= 1073 K to prepare precursors with various oxygen compositions: Ce2Zr2O7+2 delta (0.111 < delta < 0.379). Metastable tetragonal t'(meta)-(Ce0 5Zr0.5)O-2 phases were prepared by oxidizing in O-2 at 873 K the precursors, and subjected to evolved oxygen gas analysis by heating the samples at a constant rate. When the precursor was prepared at T-red = 773 K, i.e. delta = 0.379, the oxygen release behavior of the tetragonal phase agreed approximately with that of the t'. For delta < 0.29, distinct features of the t'(meta)-(Ce0 5Zr0.5)O-2 appeared in the XRD results and Raman spectra. The temperature exhibiting the maximum release rate of oxygen from the t'(meta) became lower with decreasing the delta value. It could be concluded that the thermodynamic behavior of the t'(meta) is related closely to the precursor composition and becomes more unstable with decrease in the delta value. The t' and t'(meta) phases with disordered arrangement of Ce and Zr ions may belong to the same space group; nevertheless, difference in the random arrays of the Ce and Zr ions was suggested on the basis of the present experimental results. (C) 2001 Elsevier Science Ltd. All rights reserved.