Ordered perovskites in the A{sup 2+}(Li{sub 1/4}Nb{sub 3/4})O{sub 3}-A{sup 2+}(Li{sub 2/5}W{sub 3/5})O{sub 3} (A{sup 2+}=Sr, Ca) systems
Journal Article
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· Journal of Solid State Chemistry
- Department of Materials Science and Engineering, University of Pennsylvania, 3231 Walnut St., Philadelphia, PA 19104-6272 (United States)
Single-phase 1:2 B-site ordered perovskites are formed in the (1-x)A{sup 2+}(Li{sub 1/4}Nb{sub 3/4})O{sub 3}-(x)A{sup 2+}(Li{sub 2/5}W{sub 3/5})O{sub 3} systems, A{sup 2+}=Sr and Ca, within the range 0.238=<x=<0.333. The X-ray and electron diffraction patterns are consistent with a P2{sub 1}/c monoclinic supercell, a=6ac, b=2ac, c=32ac, {beta}{approx}125 deg., where the 1:2 order is combined with b{sup -}b{sup -}c{sup +} octahedral tilting. Rietveld refinements of the ordered A(B{sup I}{sub 1/3}B{sup II}{sub 2/3})O{sub 3} structures give a good fit to a model with B{sup I} occupied by Li and Nb, B{sup II} by W and Nb, and a general stoichiometry (Sr,Ca)(Li{sub 3/4+y/2}Nb{sub 1/4-y/2}){sub 1/3}(Nb{sub 1-y}W{sub y}){sub 2/3}O{sub 3}, y=0.9x=0.21-0.30. The Sr system also includes regions of stability of a 1:3 ordered phase for 0.0=<x=<0.111, and a 1:1 ordered double perovskite for 0.833=<x=<1.0. The formation of the non-stoichiometric 1:2 ordered phases is associated with the large site charge/size differences that can be accessed in these systems, and restricted by local charge imbalances at the A-sites for W-rich compositions. These concepts are used to generate stability maps to rationalize the formation of the known 1:2 ordered oxide perovskites.
- OSTI ID:
- 20658209
- Journal Information:
- Journal of Solid State Chemistry, Journal Name: Journal of Solid State Chemistry Journal Issue: 11 Vol. 177; ISSN 0022-4596; ISSN JSSCBI
- Country of Publication:
- United States
- Language:
- English
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