Bi3n+1Ti7Fe3n–3O9n+11 Homologous Series: Slicing Perovskite Structure with Planar Interfaces Containing Anatase-like Chains

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• 作者：Dmitry Batuk ; Alexander A. Tsirlin ; Dmitry S. Filimonov ; Konstantin V. Zakharov ; Olga S. Volkova ; Alexander Vasiliev ; Joke Hadermann ; Artem M. Abakumov
• 刊名：Inorganic Chemistry
• 出版年：2016
• 出版时间：February 1, 2016
• 年：2016
• 卷：55
• 期：3
• 页码：1245-1257
• 全文大小：1210K
• ISSN：1520-510X

文摘

The n = 3–6 members of a new perovskite-based homologous series Bi_3n+1Ti₇Fe_3n–3O_9n+11 are reported. The crystal structure of the n = 3 Bi₁₀Ti₇Fe₆O₃₈ member is refined using a combination of X-ray and neutron powder diffraction data (a = 11.8511(2) ?, b = 3.85076(4) ?, c = 33.0722(6) ?, S.G. Immm), unveiling the partially ordered distribution of Ti⁴⁺ and Fe³⁺ cations and indicating the presence of static random displacements of the Bi and O atoms. All Bi_3n+1Ti₇Fe_3n–3O_9n+11 structures are composed of perovskite blocks separated by translational interfaces parallel to the (001)_p perovskite planes. The thickness of the perovskite blocks increases with n, while the atomic arrangement at the interfaces remains the same. The interfaces comprise chains of double edge-sharing (Fe,Ti)O₆ octahedra connected to the octahedra of the perovskite blocks by sharing edges and corners. This configuration shifts the adjacent perovskite blocks relative to each other over a vector ¹/₂[110]_p and creates S-shaped tunnels along the [010] direction. The tunnels accommodate double columns of the Bi³⁺ cations, which stabilize the interfaces owing to the stereochemical activity of their lone electron pairs. The Bi_3n+1Ti₇Fe_3n–3O_9n+11 structures can be formally considered either as intergrowths of perovskite modules and polysynthetically twinned modules of the Bi₂Ti₄O₁₁ structure or as intergrowths of the 2D perovskite and 1D anatase fragments. Transmission electron microscopy (TEM) on Bi₁₀Ti₇Fe₆O₃₈ reveals that static atomic displacements of Bi and O inside the perovskite blocks are not completely random; they are cooperative, yet only short-range ordered. According to TEM, the interfaces can be laterally shifted with respect to each other over ±1/3a, introducing an additional degree of disorder. Bi₁₀Ti₇Fe₆O₃₈ is paramagnetic in the 1.5–1000 K temperature range due to dilution of the magnetic Fe³⁺ cations with nonmagnetic Ti⁴⁺. The n = 3, 4 compounds demonstrate a high dielectric constant of 70–165 at room temperature.