Superspace Group Approach to the Crystal Structure of Na0.5CoO2

概要

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The crystal structure of layered cobalt oxide Na0.5CoO2 has been determined by means of the ($3+1$)-dimensional superspace group approach. Structural parameters have been refined with a superspace group of $Ccmm(1 p0)000$ using powder neutron diffraction data collected below room temperature. The compound can be regarded as a misfit-layered cobalt oxide which consists of [Na] and [CoO2] subsystems, with a refined misfit parameter $ p=b_{\text{CoO$_{2}$}}/b_{\text{Na}}=0.5011(7)$ at 296 K. A parallel set of zigzag arrangements, i.e., the positional modulation, of Na ions has been revealed along the $b$-axis. The temperature-dependent alteration of Co–O distances shows discontinuous characteristics below the phase transition temperature around 80 K, which indicates the charge-separation of Co ions. On the basis of the bond valence sum calculation, a one-dimensional charge-separation pattern of Co ions with charges of $+3.5+\delta$ and $+3.5-\delta$, perpendicular to the Na zigzag chains, is established.
Published by the Japan Society of Applied Physics through the Institute of Pure and Applied Physicsの論文
2007-01-15