Tetragonal CaF2-related-type t′-(Ce0.5Zr0.5)O2 phase was reduced at 773 K ≤ Tred. ≤ 1073 K to prepare precursors with various oxygen compositions: Ce2Zr2O7+2δ (0.111 < δ < 0.379). Metastable tetragonal t′meta-(Ce0.5Zr0.5)O2 phases were prepared by oxidizing in O2 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 Tred. = 773 K, i.e. δ = 0.379, the oxygen release behavior of the tetragonal phase agreed approximately with that of the t′. For δ < 0.29, distinct features of the t′meta-(Ce0.5Zr0.5)O2 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 δ 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 δ 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.
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