Crystal structure of metastable κ-CeZrO 4 phase possessing an ordered arrangement of Ce and Zr ions

Abstract

A pyrochlore-type precursor having less anti-phase domain boundaries was prepared by reducing a single t′-(Ce 0.5Zr 0.5)O 2 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-CeZrO 4 phase obtained, many small and sharp superlattice diffractions, characterizing the crystal structure of the κ-CeZrO 4 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, P2 13 and P 4 3m agreed with the XRD data and also the space groups permitted the ordered arrangement Ce 4+ and Zr 4+ ions along with 〈110〉 direction similar to the pyrochlore-type precursor. Finally, it was found from Rietveld analysis that the κ-CeZrO 4 phase belongs to the space group of P2 13 . In the ZrO 8 polyhedron of the κ-CeZrO 4, 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 Zr 4+ ions. A pair of enantiomorphic coordinates belonging to the same space group of P2 13 was appeared for the κ-CeZrO 4.