59Co NMR study of the Co states in superconducting and anhydrous cobaltates

59 Co NMR spectra in oriented powders of the superconducting (HSC) Na 0 . 35 CoO 2 ,1.3H 2 O and Na 0 . 35 CoO 2 compounds reveal a single electronic Co state with identical T independent NMR shift tensor. These phases differ markedly from Na 0 . 7 CoO 2 , in which we resolve 3 types of Co sites. The large T variation of their spin susceptibilities χ s and the anisotropy of the orbital susceptibility χ orb allow us to conclude that charge disproportionation occurs, in a non magnetic Co 3+ and two magnetic sites with about 0.3 and 0.7 holes in the t 2 g multiplet. The data are consistent with those for the single Co site in the anhydrous and HSC phase assuming the expected Co 3 . 65+ charge.