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.

4 pages, to appear in Phys. Rev. Lett

References in corpus (6)

• Evidence of a single nonmagnetic Co3+ state in the Na1CoO2 cobaltate
• Na Induced Correlations in Na${}_x$CoO${}_2$
• NMR Observation of Rattling Phonons in the Pyrochlore Superconductor KOs2O6
• Electronic Correlations in CoO2, the Parent Compound of Triangular Cobaltates
• Direct link between low temperature magnetism and high temperature sodium order in NaxCoO2
• Itinerant and localized magnetism on the triangular lattice: sodium rich phases of Na${}_x$CoO${}_2$

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• Crystal-to-stripe reordering of sodium ions in NaxCoO2 (x>=0.75)
• Na order and Co charge disproportionation in Na${}_x$CoO${}_2$
• 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${}_2$
• Pinball liquid phase from Hund's coupling in frustrated transition metal oxides
• Evidence for Oxygen Holes due to d-p Rehybridization in Thermoelectric Sr_{1-x}Rh_{2}O_{4}
• Complex magnetic differentiation of cobalts in Na${}_x$CoO${}_2$ with 22K Néel temperature
• Transition from a phase-segregated state to single-phase incommensurate sodium ordering in Na_xCoO_2 with x \approx 0.53