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Bi 1- x Ca x MnO 3 ( x = 0.4 and 0.45): X-ray Single-Crystal and Electron Microscopy Study

2006; American Chemical Society; Volume: 18; Issue: 14 Linguagem: Inglês

10.1021/cm060222h

1520-5002

M. Giot, Přemysl Beran, Olivier Pérez, S. Malo, M. Hervieu, B. Raveau, M. Nevřiva, K. Knı́žek, Pascal Roussel,

Advanced Condensed Matter Physics

The superstructure of Bi1-xCaxMnO3 (x = 0.4 or 0.45), which exhibits a charge/orbital-ordered state at room temperature (TCO ≈ 330 K), has been successfully determined at different temperatures using single-crystal X-ray diffraction data and the superspace formalism. This peculiar approach provides a very 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 several other techniques (electron diffraction, high-resolution electron microscopy (HREM), and synchrotron high-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 structural model is based on the alternation of one double band of Mn(1)O6 octahedra and one double band of Mn(2)O6 octahedra, the two octahedron types exhibiting almost similar distortion. HREM images were then simulated from the refined atomic positions; the good agreement with the experimental images confirms the model. Finally, the relationships between structural characterizations and magnetic properties have been investigated for these compounds.