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|Title: ||Composition- and temperature-dependent phase transitions in 1:3 ordered perovskites Ba4-xSrxNaSb3O12.|
|Authors: ||Zhou, QD|
|Issue Date: ||Nov-2007|
|Citation: ||Zhou, Q. D., Kennedy, B. J., Elcombe, M. M., & Withers, R. L. (2007). Composition- and temperature-dependent phase transitions in 1:3 ordered perovskites Ba4-xSrxNaSb3O12. Journal of Solid State Chemistry, 180(11), 3082-3092.|
|Abstract: ||A series of 25 members of the 1:3 ordered perovskite family of the type Ba4-xSrxNaSb3O12 has been synthesized and their structures determined using synchrotron X-ray and neutron powder diffraction techniques. At room temperature the sample Ba4NaSb3O12 has a cubic structure in space group Im (3) over barm with a = 8.2821(1) angstrom, where the Na and Sb cations are ordered in the octahedral sites but there is no tilting of the (Na/Sb)O-6 octahedra. As the average size of the A-site cation decreases, through the progressive replacement of Ba by Sr, tilting of the octahedra is introduced firstly lowering the symmetry to tetragonal in P4/mnc then to orthorhombic in Cmca and ultimately a monoclinic structure in P2(1)/n as seen for Sr4NaSb3O12 with a = 8.0960(2) angstrom, b = 8.0926(2) angstrom, c = 8.1003(1) angstrom and β = 90.016(2)degrees. The powder neutron diffraction studies show that the orthorhombic and tetragonal phases in Cmca and P4/mnc co-exist at room temperature for samples with x between 1.5 and 2. © 2007, Elsevier Ltd.|
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