Oxygen-deficient perovskites are a family of important materials that may exhibit oxide ionic conductivities. We attempted to introduce oxygen-vacancy disordering in perovskite CaGaNbO (Ca-type) by substituting Ca with larger Sr. Sr-to-Ca substitution did not lead to oxygen-vacancy ordering-disordering transition but an interesting Ca-to-Sr type structure transition. Rietveld refinements revealed that the two-type structures exhibit similar oxygen-vacancy ordering and identical 1:1:1 triple-cation B-site ordering. Close inspection of the two-type structures revealed the subtle structure difference lies in the orientations of GaO tetrahedra, which is the origin of the formation of the narrow two-phase region (0.3 ≤ < 0.65) in Ca Sr GaNbO. More importantly, the A- and B-site cavities with large differences in size for both structures resulted in a site-selective doping behaviour for Sr in Ca Sr GaNbO. These structural changes found in Ca Sr GaNbO will provide a broad route approaching new oxygen-deficient phases with oxide ionic conductivities.
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| http://dx.doi.org/10.1039/c9ra09970k | DOI Listing |
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