A-site cation ordering in AA'BB'O{sub 6} perovskites
- Ohio State University, Department of Chemistry, 100 West 18th Avenue, Columbus, OH 43210-1185 (United States)
Unlike ordering of the octahedral B-site cations, ordering of the larger A-site cations in stoichiometric perovskites is rare. Herein the A- and B-site ordering characteristics of several double perovskites with AA'BB'O{sub 6} stoichiometry have been investigated. The compounds investigated include NaLaMgWO{sub 6}, NaLaMgTeO{sub 6}, NaLaScNbO{sub 6}, NaLaScSbO{sub 6}, NaLaTi{sub 2}O{sub 6}, and NaLaZr{sub 2}O{sub 6}. Group theoretical methods are used to enumerate the possible structures of AA'BB'X{sub 6} double perovskites that result from the combination of rock salt ordering of the B-site cations, layered ordering of the A-site cations, and octahedral tilting distortions. This combination results in 12 possible structures in addition to the aristotype. Among the compounds investigated only NaLaMgWO{sub 6} and NaLaScNbO{sub 6} show significant long-range ordering of the A-site cations, Na{sup +} and La{sup 3+}. A complete structural characterization is presented for NaLaMgWO{sub 6}. This compound possesses monoclinic C2/m (12) space group symmetry, with unit cell dimensions of a=7.8074(1)A, b=7.8158(1)A, c=7.8977(1)A, {beta}=90.136(1){sup o} at room temperature. The results presented here show that in AA'BB'O{sub 6} perovskites layered ordering of A-site cations creates a bonding instability that is compensated for by a second-order Jahn-Teller distortion of the B' cation. These two distortions are synergistic and the removal of one leads to the disappearance of the other.
- OSTI ID:
- 20784959
- Journal Information:
- Journal of Solid State Chemistry, Vol. 179, Issue 4; Other Information: DOI: 10.1016/j.jssc.2006.01.005; PII: S0022-4596(06)00012-0; Copyright (c) 2006 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0022-4596
- Country of Publication:
- United States
- Language:
- English
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