Sodium ion dynamics in the nonstoichiometric layer-type oxide Na0.67Ni0.33Ti0.67O2 studied by Na-23 NMR

Sodium ion dynamics in the nonstoichiometric layer-type oxide Na0.67Ni0.33T i0.67O2 powder was studied by Na-23 NMR techniques. Even though 23Na is a q uadrupole nucleus, the spectra are dominantly governed by magnetic suscepti bility anisotropy of paramagnetism rather than quadrupole interaction. The static resonance line becomes narrower at higher temperature manifesting mo tional narrowing. The line shape is not axially symmetric below 270 K but b ecomes symmetric at higher temperature. This indicates that the Na+ motion is faster than 10(-8) s and isotropic in two-dimension above 270 K resultin g in averaging out the anisotropy in the ab-planes. Two different prismatic ally coordinated Na sites of the sample are reported by XRD but the fast an d isotropic Na motion in the ab-planes averages out the locational differen ce in the NMR spectra. At lower temperature, the Na+ motion slows down and becomes anisotropic in the ab-planes enough to see the anisotropy in the pl ane. (C) 2000 Published by Elsevier Science Ltd.