Cerium zirconium oxides with the composition CeZrO4 were prepared by oxidizing in O2 at 873 K precursors with the composition CeZrO3.5+δ (δ<0.3). The precursors were prepared by reducing the t′-(Ce0.5Zr0.5)O2 phase at 873≤Tred.≤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 1323≤Tred.≤1573 K, the precursors were identified as having the pyrochlore-type Ce2Zr2O7+2δ phase with δ<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 κ-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 κ phase 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+δ)/2 phases with 0.1<δ<0.3 were obtained. When the precursor obtained at Tred.=1123 K was oxidized, a tetragonal phase appeared, but its Raman spectrum was different from that seen in the t′ phase. This phase was identified to be a novel t′meta-(Ce0.5Zr0.5)O2 phase, because it transformed into the t′ phase by annealing above 1173 K under an O2 atmosphere. When the precursor obtained at Tred.=873 K was oxidized, the t′-(Ce0.5Zr0.5)O2 phase identical to the starting sample appeared. The structural difference between t′meta and t′ phases was estimated to be in their oxygen parameter, z, for the 4d site in the space group of P42/nmc. The oxygen parameter for the t′meta phase is closer to 0.25 than that for t′ phase. It was shown that the temperature and holding time for precursor preparation and the oxygen content δ are important factors for the structure of the reoxidized CeZrO4 compound.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Ceramics and Composites
- Condensed Matter Physics
- Physical and Theoretical Chemistry
- Inorganic Chemistry
- Materials Chemistry