59Co NMR study of the Co states in superconducting and anhydrous cobaltates -: art. no. 247602

Co-59 NMR spectra in oriented powders of Na0.35CoO2 and in its hydrated superconducting (HSC) phase Na0.35CoO2,1.3H(2)O reveal a single electronic Co state with identical T independent NMR shift tensor. These phases differ markedly from Na0.7CoO2, in which we resolve three types of Co sites. The large T variation of their spin susceptibilities chi(s) and the anisotropy of the orbital susceptibility chi(orb) allow us to conclude that charge disproportionation occurs in a nonmagnetic Co3+ and two magnetic sites with about 0.3 and 0.7 holes in the t(2g) multiplet. The data are consistent with those for the single Co site in the anhydrous and HSC phase assuming the expected Co3.65+ charge.