Crystal structure of metastable κ-CeZrO₄ phase possessing an ordered arrangement of Ce and Zr ions

A pyrochlore-type precursor having less anti-phase domain boundaries was prepared by reducing a single t′-(Ce_0.5Zr_0.5)O₂ phase at 1573 K. Its oxidation at 873 K proceeded leaving the ordered arrangement of Ce and Zr ions. In the powder X-ray diffraction (XRD) pattern of the metastable κ-CeZrO₄ phase obtained, many small and sharp superlattice diffractions, characterizing the crystal structure of the κ-CeZrO₄ phase, were observed in addition to the diffractions observed in the pyrochlore-type precursor. All the diffraction peaks could be indexed on the basis of the cubic lattice with a = 1.05270 nm. The condition limiting possible diffractions for space groups of P23, P2₁3 and P4̄3m agreed with the XRD data and also the space groups permitted the ordered arrangement Ce⁴⁺ and Zr⁴⁺ ions along with 〈110〉 direction similar to the pyrochlore-type precursor. Finally, it was found from Rietveld analysis that the κ-CeZrO₄ phase belongs to the space group of P2₁3. In the ZrO₈ polyhedron of the κ-CeZrO₄, long and short Zr-O bonds compared with the average Zr-O bond length existed. The long and short Zr-O bonds may relax the compulsive 8-fold coordination of Zr⁴⁺ ions. A pair of enantiomorphic coordinates belonging to the same space group of P2₁3 was appeared for the κ-CeZrO₄.