Na-23 and Co-59 NMR studies in metallic NaCo2O4

The results of Co-59 NMR studies in the metallic NaCo2O4 system reveal the existence of both diamagnetic Co3+ and magnetic Co4+ ions in the unit cell. Moreover, there are two inequivalent Co3+ ions in the ratio 2:1. The inequ ivalency of the cobalt ions can be explained from the crystallographic stru cture. A qualitative estimation of the electric field gradient at different cobalt and sodium sites has been made by the point charge model. Na-23 NMR performed in the temperature range 300 to 100 K reveals a linear variation of K-iso against chi(d)(T) in the range 220 to 100 K.