Ordering of CeIII/CeIVand Interstitial Oxygens in CeTaO4+x(x≈0.17) Superstructure

✍ Scribed by John G. Thompson; A.David Rae; Nina Bliznyuk; Ray L. Withers

• Publisher: Elsevier Science
• Year: 1999
• Tongue: English
• Weight: 352 KB
• Volume: 144
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1998.8030

✦ Synopsis

A structural model for CeTaO 4؉x (x+0.17) or alternately Ce III 4 Ce IV 2 Ta 6 O 25 (monoclinic, P2 1 , a ‫؍‬ 7.616(2), b ‫؍‬ 16.459(5), c ‫؍‬ 7.704(2) A > , ‫؍‬ 102.48(2)3, Z ‫؍‬ 2) is derived from X-ray powder di4raction data. The starting model was a 3; ;b superstructure of CeTaO 4؉x (x ‫؍‬ 0.0) with excess oxygen atoms occupying interstices between the Ce atom layers consistent with the electron di4raction determined space group symmetry P2 1 . Unexpectedly, the four Ce atoms surrounding the interstitial oxygen are not oxidized. During the re5nement the model was forced to be chemically plausible by restraining bond valence sums, bond lengths, and O+O distances. This was necessary due to the very weak scattering contribution to the XRD pro5le by oxygen atoms. The mechanism for oxidation of the subject phase from CeTaO 4؉x (x ‫؍‬ 0.0) is discussed and a reason for the limiting composition for this phase is proposed.