Electronic texture of the thermoelectric oxide Na0.75CoO2

M. -H. Julien (1) , C. de Vaulx (1) , H. Mayaffre (1) , C. Berthier (1, 2) , M. Horvatic (2) , Virginie Simonet (3) , J. Wooldridge (4) , G. Balakrishnan (4) , M. R. Lees (4) , D. P. Chen (5) , C. T. Lin (5) , Pascal Lejay (6)

1 LSP - Laboratoire de Spectrométrie Physique
2 LCMI-GHMFL - Laboratoire des champs magnétiques intenses
3 NEEL - MagSup - Magnétisme et Supraconductivité
4 Department of Physics [Coventry]
5 Max Planck Institute for Solid State Research
6 NEEL - C2MA - Croissance Cristalline et MicroAnalyse

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.

Domaines: Autre [cond-mat.other]

M. -H. Julien, C. de Vaulx, H. Mayaffre, C. Berthier, M. Horvatic, et al.. Electronic texture of the thermoelectric oxide Na0.75CoO2. Physical Review Letters, 2008, 100, pp.096405. ⟨10.1103/PhysRevLett.100.096405⟩. ⟨hal-00268870⟩