Sodium Ion Mobility in NaxCoO2 (0.6 < x < 0.75) Cobaltites Studied by 23Na MAS NMR

Abstract
Various P2 and P′3-NaxCoO2 phases, with x ranging approximately from 0.6 to 0.75, have been studied by variable-temperature 23Na magic angle spinning (MAS) NMR. Signal modification versus temperature plots clearly show that Na+ ions are not totally mobile at room temperature on the NMR time scale. As the temperature increases, the line shape change of the 23Na MAS NMR signal differs for the P2 and P′3 stackings and is interpreted by the differences of Na+ ion sites and of sodium diffusion pathways in the two structures.