Defect structure of nominally pure lithium niobate crystals grown from a boron doped charge have been studied by Raman and optical spectroscopy, laser conoscopy, and photoinduced light scattering. An influence of boron dopant on optical uniformity, photoelectrical fields values, and band gap have been also studied by these methods in LiNbO₃ crystals. Despite a high concentration of boron in the charge (up to 2 mol%), content in the crystal does not exceed 10⁻⁴ wt%. We have calculated that boron incorporates only into tetrahedral voids of crystal structure as a part of groups [BO₃]³⁻, which changes O–O bonds lengths in O₆ octahedra. At this oxygen–metal clusters MeO₆ (Me: Li, Nb) change their polarizability. The clusters determine optically nonlinear and ferroelectric properties of a crystal. Chemical interactions in the system Li₂O–Nb₂O₅–B₂O₃ have been considered. Boron, being an active element, structures lithium niobate melt, which significantly influences defect structure and physical properties of a crystal grown from such a melt. At the same time, amount of defects Nb_Li and concentration of OH groups in LiNbO₃:B is close to that in stoichiometric crystals; photorefractive effect, optical, and compositional uniformity on the contrary is higher.

Two series of LiNbO₃:Mg:B crystals have been grown and studied. Two doping methods—have been used. The crystals—have been co-doped with Mg and a non-metallic dopant, B. The physicochemical features of the growth—have been considered for LiNbO₃:Mg:B crystals obtained from a boron-doped melt. The charge—has been prepared using different technologies: homogeneous (HG) and solid-phase (SP) doping. The same two methods have been used to grow single-doped LiNbO₃:Mg crystals. A control near-stoichiometric (NSLN) crystal—has been grown via the HTTSSG (high-temperature top-seeded solution growth) method from a congruent melt (Li/Nb ≈ 0.946) with 5.5 wt% K₂O. The characteristics of the LiNbO₃:Mg:B crystals—have been compared with those of the LiNbO₃:Mg and NSLN crystals. Physicochemical and structural reasons have been established for the differences in the distribution coefficients of magnesium (K_D) during the growth of the HG- and SP-doped LiNbO₃:B:Mg and LiNbO₃:Mg crystals. The optical characteristics of the LiNbO₃:B:Mg crystals—have been studied via optical spectroscopy, laser conoscopy and photoinduced light scattering (PILS). The influence of boron on the microstructure, compositional and optical uniformities and optical damage resistance of the LiNbO₃:Mg:B crystals—has been estimated. Optimal technological approaches to growing optically uniform LiNbO₃:B:Mg crystals have been determined. LiNbO₃:Mg:B crystals have been shown to have a significant advantage over the commercially used LiNbO₃:Mg crystals since large LiNbO₃:Mg:B crystals can be grown without stripes. Such stripes usually appear perpendicular to the growth axis. In addition, the photorefractive effect is suppressed in LiNbO₃:Mg:B crystals at lower magnesium concentrations ([Mg] ≈ 2.5 mol%) than in LiNbO₃:Mg ([Mg] ≈ 5.5 mol%).

We have studied the macro-and microstructure and properties of LiNbO3〈B〉 crystals in comparison with LiNbO3〈Zn〉 and stoichiometric and congruent lithium niobate crystals. The optical characteristics...

Physical and chemical properties have been studied in lithium niobate (LiNbO₃, LN) crystals grown by Czochralski from a boron doped melt. Optical uniformity and optical damage resistance of LiNbO₃:B crystals have been compared with control crystals of nominally pure congruent (CLN) and near-stoichiometric (NSLN K₂O) composition. LiNbO₃:B crystals structure has been studied. Studied LiNbO₃:B crystals have been grown from differently synthesized charges. The charges have been synthesized from a mixture Nb₂O₅:B-Li₂CO₃ using homogeneously doped Nb₂O₅:B precursor (sample 1, (B) = 0.0034 wt% in the charge) and by a direct solid phase synthesis from Nb₂O₅-Li₂CO₃-H₃BO₃ mixture (sample 2, (B) = 0.0079 wt% in the charge). Only traces of boron (10⁻⁵–10⁻⁴ wt%) have been detected in the samples. We have established that concentration of anti-site defects Nb_Li is lower in both LiNbO₃:B than in CLN crystals. XRD analysis has confirmed that B³⁺ cations localize in faces of tetrahedral voids O₄ of LN structure. The voids act as buffers at the anion sublattice distortion. Sample 1 has been shown to have a structure closer to NSLN K₂O crystal than sample 2. We have also shown that the chemical purity of LN crystal increases compared to the melt purity because boron creates strong compounds with impurities in the melt system Li₂O-Nb₂O₅-B₂O₃. Metals impurities thus stay in the melt and do not transfer to the crystal.

We have studied the effect of gamma irradiation to various doses on optical characteristics (optical transmission spectra) of nominally undoped, rare earth-doped, and alkaline earth-doped lithium niobate crystals: LiNbO₃, LiNbO₃:Y (0.46 wt %), LiNbO₃:Y,Mg (0.32, 0.24 wt %), LiNbO₃:Mg (0.27 wt %), and LiNbO₃:Gd (0.004, 0.04, 0.26, 0.43 wt %). We have examined the influence of the ionizing radiation dose, the nature of dopants, and their concentration on the optical transmission of the gamma-irradiated doped lithium niobate crystals. The results suggest that gamma-induced changes in the optical transmission of LiNbO₃:Gd (≃0.004 and 0.04 wt %) crystals can be used for gamma dosimetry in the dose range ≃10¹ to 1.5 × 10⁴ rad.