The modulated crystal structure of Bi2.12Ba 2.00Rh1.95Ox- has been studied by electron diffraction measurements and high-resolution electron microscopy. The crystal structure consists of two interpenetrating subsystems of a RhO2 sheet and a distorted four-layered rock-salt-type (Bi,Ba)O block. Both subsystems have common a- and c-axes and a β-angle with a = 5.38 Å, c = 15.15 Å and β= 95.3°. On the other hand, the crystal structure is incommensurate along the b-axes; b1 = 3.05 Å for the RhO 2 sheet and b2 = 5.45 Å for the (Bi,Ba) O block. The misfit ratio and the analytical composition give the chemical formula of [Bi1.94Ba1.83Oy]0.56[RhO 2]. This compound has two modulation vectors, q1 = -a* + 0.56b*1 and q2 = 0.11b*1 + 0.35c*, and the superspace group is assigned as a C2/m(1aα0, 0βy)-type on the basis of the systematic absence of reciprocal lattice points shown in the electron diffraction patterns. This modulation vector q 2 is different from the one in [Bi1.79Sr 1.98Oy]0.63[RhO2], which has recently been studied by the authors. An additional modulation vector, q3 = 0.12a* + 0.10b*1, is locally observed. High-resolution images taken with the incident electron beam parallel to the a- and c-axes clearly exhibit modulated atomic arrangements. This compound is characterized by not only the displacement modulation but also the concentration modulation in the rock-salt subsystem.
|ジャーナル||Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers|
|出版ステータス||出版済み - 1 10 2006|
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