An approach to the defect structure analysis of lithium niobate single crystals

A formula for calculating the soft mode frequency and Curie temperature (using ion mass, charge, and the distances between them) was applied to the analysis of the defect structure of nonstoichiometric lithium niobate. Four compositions from near stoichiometric to highly Li2O deficient, including congruent, were studied. The Curie temperatures were calculated for three possible types of defects: (1) oxygen vacancies, (2) niobium vacancies, and (3) lithium vacancies. A comparison between the calculated and experimental values showed that the oxygen and niobium vacancy models did not agree with experimental data. Good quantitative agreement between the calculated and experimental data for the lithium vacancy model allowed us to conclude that this model best describes the defect structure of nonstoichiometric lithium niobate LiNbO3.