Precession Electron Diffraction Tomography for Solving Complex Modulated Structures: the Case of Bi5Nb3O15

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• 作者：Philippe Boullay ; Lukas Palatinus ; Nicolas Barrier
• 刊名：Inorganic Chemistry
• 出版年：2013
• 出版时间：May 20, 2013
• 年：2013
• 卷：52
• 期：10
• 页码：6127-6135
• 全文大小：837K
• 年卷期：v.52,no.10(May 20, 2013)
• ISSN：1520-510X

文摘

The crystal structure of the 1D incommensurately modulated phase Bi₅Nb₃O₁₅ [superspace group X2mb(0b0)000, a = 5.46781(7) 脜, b = 5.47381(8) 脜, c = 41.9005(5) 脜, 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.