Title: Precession Electron Diffraction Tomography for Solving Complex Modulated Structures: the Case of Bi<sub>5</sub>Nb<sub>3</sub>O<sub>15</sub>
Abstract: The crystal structure of the 1D incommensurately modulated phase Bi5Nb3O15 [superspace group X2mb(0b0)000, a = 5.46781(7) Å, b = 5.47381(8) Å, c = 41.9005(5) Å, and q = 0.17588(8)b*] is solved by electron diffraction using a tomography technique combined with precession of the electron beam. The (3 + 1)D structure is further validated by a refinement against powder X-ray diffraction (PXRD). A coherent picture of the true nature of this compound is obtained, conciliating experimental observations made by different groups using transmission electron microscopy and PXRD. Bi5Nb3O15 does not have a mixed-layer Aurivillius-type structure but does contain structural elements, [Bi2O2](2+) slabs, and perovskite-like blocks, characteristic of Aurivillius phases. The presence of aperiodic crystallographic shear planes (CSPs) along the modulated direction b leads to the formation of an original layered structure containing both continuous and discontinuous [Bi2O2](2+) and perovskite-like octahedral layers. Between CSPs, the stacking of these two structural elements exhibits an unprecedented nonuniform sequence referring to Aurivillius phases.
Publication Year: 2013
Publication Date: 2013-05-01
Language: en
Type: article
Indexed In: ['crossref', 'pubmed']
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Cited By Count: 53
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