ANALYSIS OF INTRINSIC DEFECTS IN THE LITHIUM-NIOBATE STRUCTURE BY THENMR LI-7 METHOD

The analysis of a defect structure based on two well known formulas of the congruent composition of a LiNbO3 crystal has been performed. Fiv e main variants of the defect structure are considered and used for ca lculating the electric-field gradient at the Li-7 nuclei. Based on the set of the electric-field gradient tensors, the nuclear-magnetic-reso nance (NMR) spectra are simulated for the models and then compared wit h the experimentally observed ones. It is found that the best agreemen t of these data is observed for complex defects [of the type when Nb5 occupies a Li+ vacancy plus three Li+ vacancies (in the nearest envir onment) plus one independent Li+ vacancy] with due regard for mobility of the Li-7 nuclei within the octahedron LiO6 under the conditions of 3Li(2)O deficiency.