Electronic texture of the thermoelectric oxide Na0.75CoO2.
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.
Julien
M-H
MH
Laboratoire de Spectrométrie Physique, UMR5588 CNRS, 38402 Saint Martin d'Hères, France. Marc-Henri.Julien@ujf-grenoble.fr
de Vaulx
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Mayaffre
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Berthier
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Horvatić
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Simonet
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Wooldridge
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Balakrishnan
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Lees
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Chen
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Lin
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Lejay
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