STUDY OF STRUCTURAL FEATURES OF LiNbO3:Cu CRYSTALS BY IR ABSORPTION SPECTRA IN THE REGION OF STRETCHING VIBRATIONS OF HYDROGEN BONDS

Single crystals LiNbO3:Cu (0.015 wt.%) and LiNbO3:Cu (0.46 wt.%) were studied by IR absorption spectroscopy in the area of valent vibrations of OH-groups. It was found that the absorption bands in the IR spectrum are associated with related to stoichiometry disturbances in in the crystal due to the presence of point defects (VLi, NbLi) and complex VLi-OH defects formed with them. The inclusion of a copper dopant leads to a significant deformation of the oxygen octahedron due to the large ionic radius of the Cu2+ cation and an increase in the O-O lengths. A new absorption band with a frequency of 3487 cm-1, corresponding to the VLi-OH complex defect, is recorded in the IR spectrum. Calculation of the volume concentration of OH groups showed the highest value for the LiNbO3:Cu crystal (0.015 wt.%) and the lowest for LiNbO3:Cu (0.46 wt.%), which is associated with a change in the localization of copper cations in the crystal structure and the formation of complex defects : Cu3--OH and VLi-OH