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

Cerium zirconium oxides with the composition CeZrO4 were prepared by oxidizing in O2 at 873 K precursors with the composition CeZrO3.5+ (<0.3). The precursors were prepared by reducing the tʹ-(Ce0.5Zr0.5)O2 phase at 873Tred.1573 K. The CeZrO4 compounds together with the precursors were characterized by powder X-ray diffraction and IR and Raman spectroscopies. In the case of 1323Tred.1573 K, the precursors were identified as having the pyrochlore-type Ce2Zr2O7+2 phase with <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 -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 kAPPAphase was not the same as that of the pyrochlore-type structure. In the case of Tred.<1123 K, cubic CaF2-related-type (Ce0.5Zr0.5)O(3.5+DELTA)/2 phases with 0.1