Clusters in the structure of non-stochiometric lithium niobate crystals

This work examines the main reasons for the appearance of an "extra" band with a frequency of similar to 737 cm(-1) in the Raman spectra of lithium niobate crystals. The following stand out among the reasons: the presence of clusters (microstructures); the presence of microinclusions of impurity phases of other lithium niobates (LiNb3O8 and Li3NbO4); strong anharmonicity of some fundamental vibrations of the Raman spectrum. The structure of clusters differs from the structure of the crystalline matrix. It has been shown that the appearance of a line with a frequency of similar to 737 cm(-1) in the Raman spectrum cannot be unambiguously associated with the existence of regions with reduced symmetry in the structure of doped crystals. These regions are the result of uneven incorporation of dopants into the crystal. The existence of these areas is also not explained in terms of the photorefractive effect. The results of studying the features of the defect structure, stoichiometry, optical uniformity and photorefractive effect confirm a correlation between the band with a frequency of similar to 737 cm(-1) and Nb-Li defects in the structure of the lithium niobate crystal.