Electronic texture of the thermoelectric oxide Na0.75CoO2

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.

arXiv comment4 pages, to appear in Phys. Rev. Lett

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• Na-ion dynamics in Quasi-1D compound NaV2O4
• Metal-nonmetal transition in LixCoO2 thin film and thermopower enhancement at high Li concentration
• The Duel of Magnetic Interactions & Structural Instabilities: Itinerant Frustration in the Triangular Lattice Compound LiCrSe${}_2$
• Ionic Hubbard model on a triangular lattice for Na_0.5CoO_2, Rb_0.5CoO_2 and K_0.5CoO_2: Mean-field slave boson theory
• Pinball liquid phase from Hund's coupling in frustrated transition metal oxides
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• Sodium ion ordering of Na0.77CoO2 under competing multi-vacancy cluster, superlattice and domain formation