FEATURES OF THE LOCALIZATION OF DOPPING CATIONS Tb³⁺ IN A LiNbO₃ CRYSTAL IN THE CONCENTRATION RANGE 0,1-2,21 WT. %

LiNbO3:Tb (0,1 wt.%), LiNbO3:Tb (0,48 wt.%), and LiNbO3:Tb (2,21 wt.%) crystals were studied by the infrared absorption spectroscopy in the area of valence vibrations of OH--groups. These crystals were grown by Czochralski method employing direct alloying of blend of the congruent composition. It was found that when the concentration of point defect centers of the cationic sublattice V-Li was higher, than the concentration of impurity point defects Tb-Li, an absorption band with the frequency of 3487 cm(-1) was registered in the IR spectrum. This absorption band is associated with the violation of stoichiometry and the formation of a complex defect (V-Li - OH) in the LiNbO3:Tb (0,1 wt.%), and LiNbO3:Tb (0,48 wt.%) crystals. A further increase in the concentration of the alloying impurity leads to a change in the O-O bond length, which affects the OH-bond length and the appearance of a new absorption band with a frequency of 3493 cm(-1), which corresponds to the complex defect (Tb-Li - OH) in the LiNbO3 crystal. Due to non-uniform admixture in the LiNbO3:Tb crystal, clusters are formed to which the absorption bands with frequencies in the range of from 3100-3403 cm(-1) to 3510-3580 cm(-1) in the spectrum.