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A - and B - Site Order in (Na1/2La1/2)(Mg1/3Ta2/3)O3 Perovskites

Published online by Cambridge University Press:  16 February 2011

L. Dupont ,
L. Chai  and
P.K. Davies
L. Dupont
Affiliation:
Dept. of Materials Science & Engineering, University of Pennsylvania, 3231 Walnut St., Philadelphia, PA 19104-6272
L. Chai
Affiliation:
Dept. of Materials Science & Engineering, University of Pennsylvania, 3231 Walnut St., Philadelphia, PA 19104-6272
P.K. Davies
Affiliation:
Dept. of Materials Science & Engineering, University of Pennsylvania, 3231 Walnut St., Philadelphia, PA 19104-6272
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Abstract

The “1:2” family of A2+(B2+1/3B+5+2/3)O3 (e.g. B2+ = Mg, Ni, Zn; B5+ = Nb, Ta) mixed metal perovskites typically adopt a 1:2 layered ordered structure when A = Ba and Sr, and a 1:1 ordered doubled perovskite structure for A = Pb. To understand the stability of the cation order in these systems and explore how the different cation correlations affect their dielectric and ferroelectric properties, the response of several members of this family of perovskites to a series of chemical substitutions and thermal treatments have been explored. In this paper we present results for a system where the divalent A cation is replaced by a 1:1 mixture of Na+ and La3+. At all temperatures this substitution stabilizes 1:1 B-site ordering. Below ~ 950°C an additional ordering reaction occurs on the A sub-lattice with Na and La occupying alternate layers along the c axis. The formation of different orientational variants of the A-site ordered phase produces a twinned nano-domain structure which in turn perturbs the length-scale, but not the symmetry, of the order on the B-site lattice. The presence of (Na1/2La1/2) on the A-site is apparently effective in destabilizing the 1:2 layering of the B-site cations observed in alkaline earth systems, possibly through unfavorable local charge imbalances.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 547: Symposium DD – Solid-State Chemistry of Inorganic Materials II , 1998 , 93
Copyright
Copyright © Materials Research Society 1999

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