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arXiv · 0801.4095

Electronic texture of the thermoelectric oxide Na0.75CoO2

M. -H. Julien·C. de Vaulx·H. Mayaffre·C. Berthier·M. Horvatic·V. Simonet·J. Wooldridge·G. Balakrishnan·M. R. Lees·D. P. Chen·C. T. Lin·P. Lejay
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Abstract

From 59Co and 23Na NMR, we demonstrate the impact of the Na+ vacancy ordering on the cobalt electronic states in Na0.75CoO2: at long time scales, there is neither a disproportionation into 75 % Co3+ and 25 % Co4+ states, nor a mixed-valence metal with a uniform Co3.25+ state. Instead, the system adopts an intermediate configuration in which 30 % of the lattice sites form an ordered pattern of localized Co3+ states. Above 180 K, an anomalous mobility of specific Na+ sites is found to coexist with this electronic texture, suggesting that the formation of the latter may contribute to stabilizing the Na+ ordering. Control of the ion doping in these materials thus appears to be crucial for fine-tuning of their thermoelectric properties.

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M. -H. Julien, C. de Vaulx, H. Mayaffre, C. Berthier, M. Horvatic, V. Simonet, J. Wooldridge, G. Balakrishnan, M. R. Lees, D. P. Chen, C. T. Lin, P. Lejay. 2008-01-26. Electronic texture of the thermoelectric oxide Na0.75CoO2. https://doi.org/10.1103/physrevlett.100.096405

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