Synthesis of Homogeneous Doping with Zinc Charge of Lithium Niobate and Comparative Study of LiNbO₃:Zn Crystals of Different Genesis

Abstract—The congruent charge LiNbO₃:Zn (2.44 wt %) was synthesized using precursor Nb₂O₅:Zn (2.83 wt %) by the method of homogeneous doping. The LiNbO₃:Zn crystal (2.12 wt %) was grown from this charge by the Czochralski method. The crystal demonstrates high chemical uniformity of Zn dopant distribution along the growth axis. The same distribution is characteristic of crystals obtained by usual direct doping. The homogeneously doped LiNbO₃:Zn crystal (2.12 wt %) and the LiNbO₃:Zn (2.02 wt %), LiNbO₃:Zn (2.05 wt %), and LiNbO₃:Zn (2.12 wt %) crystals close to this composition obtained by method of direct doping, as well as LiNbO_(3cong), were compared to study defectiveness and optical and structural homogeneity. The method of IR absorption spectroscopy, photoinduced light scattering, and laser conoscopy were used for the study. All studied crystals show no photorefractive response, as can be seen from photoinduced light scattering. The conoscopic patterns of a crystal LiNbO₃: Zn (2.12 wt %, homogeneous doping) are strained, which can be connected with a greater photoinduced ability to scatter light than in other crystals. The ability is caused by microstructures, clusters, and residual domain structures. However IR spectra demonstrate narrowing of bands, which can be explained by the fact that homogeneous doping of a Nb₂O₅ precursor with zinc contributes to the ordering of the lithium sublattice of a LiNbO₃:Zn crystal and ordering of H⁺ protons compared to the ordering in a LiNbO_3cong crystal. This effect is highly unusual at this concentration of the dopant.