Investigation of the structural features of LiNbO3:Gd (0.002-0.26 wt.%) crystals by IR absorption spectra in the region of valence vibrations of hydrogen bonds

Nonlinearly optical single crystals LiNbO3:Gd (0.001-0.26 wt.%) were grown by the Czochralskii method using the technology of direct doping charge of congruent composition. The defect structure of crystals in the region of valence vibrations of hydrogen bonds was studied by IR absorption spectroscopy. It was found that in the region of small concentrations of the doping impurity gadolinium on the IR spectrum there is a decrease in the widths of absorption bands. The gadolinium impurity with the concentration of 0.26 wt.% leads to a significant deformation of the oxygen octahedron due to the large ionic radius of the gadolinium cation and an increase in the O-O length. A new absorption band at 3488 cm-1 corresponding to the VLi-OH complex defect is registered on the IR spectrum. The calculation of the volume concentration of OH-groups showed the lowest value for LiNbO3congr crystal and the highest for LiNbO3:Gd(0.005 wt.%), which is related to the process of doping impurity entring into the structure and the increase in the number of point defect centers VLi necessary to compensate the structural defect GdLi2+