Crystal structure of metastable K-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'-(Ce0.5Zr0.5)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 kappa -CeZrO4 phase obtained, many small and sharp superlattice diffractions, characterizing the crystal structure of the kappa -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, P2(1)3 and P (4) over bar 3m 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 kappa -CeZrO4 phase belongs to the space group of P2(1)3. In the ZrO8 polyhedron of the kappa -CeZrO4, long and short Zr-O bends 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 P2(1)3 was appeared for the kappa -CeZrO4. (C) 2000 Elsevier Science B.V. All rights reserved.