Crystal Structure of Misfit-Layered Compound [Bi1.94Ba1.83Oy]0.56[RhO2]

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The modulated crystal structure of Bi2.12Ba2.00Rh1.95Ox 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 $\beta$-angle with $a=5.38$ Å, $c=15.15$ Å and $\beta=95.3$°. On the other hand, the crystal structure is incommensurate along the $b$-axes; $b_{1}=3.05$ Å for the RhO2 sheet and $b_{2}=5.45$ Å for the (Bi,Ba)O block. The misfit ratio and the analytical composition give the chemical formula of [Bi1.94Ba1.83Oy]0.56[RhO2]. This compound has two modulation vectors, $\mathbf{q}_{1}=-\mathbf{a}^{*}+0.56\mathbf{b}_{1}^{*}$ and $\mathbf{q}_{2}=0.11\mathbf{b}_{1}^{*}+0.35\mathbf{c}^{*}$, and the superspace group is assigned as a $C2/m(1\alpha 0,0\beta\gamma)$-type on the basis of the systematic absence of reciprocal lattice points shown in the electron diffraction patterns. This modulation vector $\mathbf{q}_{2}$ is different from the one in [Bi1.79Sr1.98Oy]0.63[RhO2], which has recently been studied by the authors. An additional modulation vector, $\mathbf{q}_{3}=0.12\mathbf{a}^{*}+0.10\mathbf{b}_{1}^{*}$, 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.
Published by the Japan Society of Applied Physics through the Institute of Pure and Applied Physicsの論文
2006-01-15

Crystal Structure of Misfit-Layered Compound [Bi1.94Ba1.83Oy]0.56[RhO2]

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