7Li NMR STUDY ON SURFACE IONIC DIFFUSION IN NANOCRYSTALLINE LiNbO3

By a wet chemical method we have prepared nano-LiNbO3 with different crystallite sizes. Their 7Li NMR spectra each show, on top of a broad band accompanied by two satellites, a sharp central peak whose strength decreases with growing grain size. On the other hand, for a given sample and as temperature rises, the separation between the two satellites gets wider, but the sharp peak gets narrower. From the satellite splitting we may estimate the molar ratio [Li]/[Nb] inside the nanocrystals, and this ratio is seen to be nearer to unity in a sample of smaller grain size. The sharp peak, indiscernible in bulk (mono- or microcrystalline) LiNbO3, is attributed to Li ions in the disproportionally large surface regions of our samples. The narrowness of its linewidth arises from the fast diffusion of these ions caused by high oxygen deficiency on the surface.