Modulated Structure of Misfit-Layered Compound [Bi2.08Sr1.67Oy]0.54[CoO2]

概要

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The modulated structure of Bi2.49Sr2.00Co2.22Ox is studied by electron diffraction analysis and high-resolution electron microscopy. The crystal structure consists of two interpenetrating subsystems of a CoO2 sheet and a distorted four-layered rock-salt-type (Bi,Sr)O block. Both subsystems have common $a$-axes, $c$-axes and $ \beta $-angles with $a=4.99$ Å, $c=15.25$ Å, and $ \beta=93.6$°. On the other hand, the crystal structure is incommensurately modulated parallel to the $b$-axis, in which $b_{1}=2.78$ Å for the CoO2 sheet and $b_{2}=5.12$ Å for the (Bi,Sr)O block, respectively. These vectors characterize the structural analogue as [Bi2.08Sr1.67Oy]0.54[CoO2]. It is found that this compound has various modulation vectors, $\mathbf{q}_{1}=-\mathbf{a}^{*}+0.54\mathbf{b}_{1}^{*}$, $\mathbf{q}_{2}=0.05\mathbf{b}_{1}^{*}$ and locally $\mathbf{q}_{3}=-0.14\mathbf{a}^{*}+0.10\mathbf{b}_{1}^{*}$. The intrinsic modulation vector $\mathbf{q}_{2}$ is different from that in [Bi0.87SrO2]2[CoO2]1.82 studied by Leligny et al. High-resolution images taken with the incident electron beam parallel to the $a$- and $c$-axes clearly exhibit modulated atomic arrangements. The local modulation mode characterized by the vector $\mathbf{q}_{3}$ is associated with the shear deformation in the $a$–$b$ plane.
Published by the Japan Society of Applied Physics through the Institute of Pure and Applied Physicsの論文
2006-05-15