VIBRATIONAL SPECTROSCOPIC AND X-RAY DIFFRACTION STUDIES OF CERIUM ZIRCONIUM OXIDES WITH Ce/Zr COMPOSITION RATIO=1 PREPARED BY REDUCTION AND SUCCESSIVE OXIDATION OF t'-(Ce0.5Zr0.5)O2 PHASE

摘要

Cerium zirconium oxides with the composition CeZrO4 were prepared by oxidizing in O2 at 873 K precursors with the composition CeZrO3.5+delta (delta<0.3). The precursors were prepared by reducing the t'-(Ce0.5Zr0.5)O2 phase at 873 less than or equal to Tred. less than or equal to 1573 K. The CeZrO4 compounds together with the precursors were characterized by powder XRD and IR and Raman spectroscopies. In the case of 1323 less than or equal to Tred. less than or equal to 1573 K, the precursors were identified as having the pyrochlore-type Ce2Zr2O7+2delta phase with delta<0.06. When the reduction temperature was decreased, the ordering level between Ce and Zr ions was decreased in the pyrochlore-type phase. The CeZrO4 compounds obtained by oxidizing the pyrochlore-type precursors were identified as the kappa-CeZrO4 phase in which Ce and Zr ions are in an ordered arrangement similar to that of the pyrochlore-type structure. The space group of the kappa phase was not the same as that of the pyrochlore-type structure. In the case of Tred. less than or equal to 1123 K, cubic CaF2-related-type (Ce0.5Zr0.5)O(3.5+delta)/2 phases with 0.1