Bi1-xCaxMnO3 (x = 0.4 and 0.45): X-ray Single-Crystal and Electron Microscopy Study

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• 作者：M. Giot ; P. Beran ; O. Pé ; rez ; S. Malo ; M. Hervieu ; B. Raveau ; M. Nevriva ; K. Knizek ; and P. Roussel
• 刊名：Chemistry of Materials
• 出版年：2006
• 出版时间：July 11, 2006
• 年：2006
• 卷：18
• 期：14
• 页码：3225 - 3236
• 全文大小：782K
• 年卷期：v.18,no.14(July 11, 2006)
• ISSN：1520-5002

文摘

The superstructure of Bi_1-xCa_xMnO₃ (x = 0.4 or 0.45), which exhibits a charge/orbital-ordered stateat room temperature (T_CO mages/entities/ap.gif"> 330 K), has been successfully determined at different temperatures usingsingle-crystal X-ray diffraction data and the superspace formalism. This peculiar approach provides avery convenient way to analyze all possible 3D symmetry (P2₁/m, Pm, and Pnm2₁) of the superstructure.The structural model of the ordered state has been confirmed thanks to complementary data from severalother techniques (electron diffraction, high-resolution electron microscopy (HREM), and synchrotronhigh-resolution X-ray powder diffraction, all vs T). It is compatible with an orthorhombic cell (a =11.002(2) Å, b = 7.588(1) Å, c = 5.425(4) Å at 150 K) and the space group Pnm2₁. The structuralmodel is based on the alternation of one double band of Mn(1)O₆ octahedra and one double band ofMn(2)O₆ octahedra, the two octahedron types exhibiting almost similar distortion. HREM images werethen simulated from the refined atomic positions; the good agreement with the experimental imagesconfirms the model. Finally, the relationships between structural characterizations and magnetic propertieshave been investigated for these compounds.