Work

Electronic Texture of the Thermoelectric Oxide Na0.75CoO2

Year: 2008

Type: article

Abstract: From $^{59}\mathrm{Co}$ and $^{23}\mathrm{Na}$ NMR, we demonstrate the impact of the ${\mathrm{Na}}^{+}$ vacancy ordering on the cobalt electronic states in ${\mathrm{Na}}_{0.75}{\mathrm{CoO}}_{2}$: at long time scales, there is neither a disproportionation into 75% ${\mathrm{Co}}^{3+}$ and 25% ${\mathrm{Co}}^{4+}$ states, nor a mixed-valence metal with a uniform ${\mathrm{Co}}^{3.25+}$ state. Instead, the system adopts an intermediate configuration in which 30% of the lattice sites form an ordered pattern of localized ${\mathrm{Co}}^{3+}$ states. Above 180 K, an anomalous mobility of specific ${\mathrm{Na}}^{+}$ sites is found to coexist with this electronic texture, suggesting that the formation of the latter may contribute to stabilizing the ${\mathrm{Na}}^{+}$ ordering. Control of the ion doping in these materials thus appears to be crucial for fine-tuning of their thermoelectric properties.

Source: Physical Review Letters

DOI: 10.1103/physrevlett.100.096405