Publication Details

Julien, M. -H., de Vaulx, C., Mayaffre, H., Berthier, C., Horvatic, M., Simonet, V., Wooldridge, J., Balakrishnan, G., Lees, M. R., Chen, D. P., Lin, C. T. & Lejay, P. (2008). Electronic texture of the thermoelectric oxide Na0.75CoO2. Physical Review Letters, 100 (9), 096405-1-096405-4.


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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