7Li NMR study of milling effects on instability of lithium-sites in lithium substituted silver niobate

Site occupation and structural change in Li substituted AgNbO3 were probed by 7Li NMR. Characteristic changes in the 7Li NMR spectra depending on Li content were observed. Analysis of integrated intensity of the spectra revealed that 16% of substituted Li+ ions occupy quasi-stable sites induced in crystal structure at 300 K in the 5 mol% Li substituted sample and would be in the state of motion, which are comparable to that of Li+ ion in LiNbO3 at high temperature. On the other hand, it was found that the Li+/Ag+ sublattice in the 12.5 mol% Li substituted sample is easily made unstable by structural disturbance introduced in structure and the instability of the sublattice stimulates a local Li+ ion motion via quasi-stable sites at room temperature. An appearance of the quasi-stable sites in local structure due to the Li substitution is closely related to instability of the Li/Ag sublattice and Li+ ion dynamics in Li substituted AgNbO3.