Crystal Structure of Thermoelectric Compound [Bi1.79Sr1.98Oy]0.63[RhO2]

概要

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We have studied the crystal structure of the misfit-layered crystal Bi1.91Sr2Rh1.77Ox by electron diffraction and high-resolution electron microscopy. This compound consists of two interpenetrating subsystems of a RhO2 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 $a=5.28$ Å, $c=29.77$ Å, and $\beta=93.7$°. On the other hand, the crystal structure is incommensurated parallel to the $b$-axis, $b_{1}=3.07$ Å for the RhO2 sheet and $b_{2}=4.88$ Å for the (Bi,Sr)O block. The axis ratio, $b_{1}/b_{2}\sim 0.63$, characterizes the structural analogue as [Bi1.79Sr1.98Oy]0.63[RhO2]. This compound has two modulation vectors, $\mathbf{q}_{1}=\mathbf{a}^{*}+0.63\mathbf{b}_{1}^{*}$ and $\mathbf{q}_{2}=0.17\mathbf{b}_{1}^{*}+\mathbf{c}^{*}$, and the superspace group is assigned as the $Cc(1\beta 0,0\mu 1)$ type from electron diffraction patterns. High-resolution images taken with the incident electron beam parallel to the $a$- and $c$-axes clearly exhibit modulated displacive as well as compositional atomic arrangements. A tentative structure model has been proposed, and the calculated image reproduces observed characteristic features reasonably well.
Published by the Japan Society of Applied Physics through the Institute of Pure and Applied Physicsの論文
2005-12-15