I. V. Biryukova

Growth of heavily doped LiNbO3〈Zn〉 crystals

We have studied conditions for the growth of LiNbO3〈Zn〉 crystals in the composition range ≃4.0–8.91 mol % ZnO. It has been shown that, in the composition range ≃4–6.8 mol % ZnO in the melt, compositionally and optically homogeneous LiNbO3〈Zn〉 crystals can be grown. Above 6.8 mol % ZnO, imperfect crystals consisting of two distinct phases grow. We have accurately determined threshold impurity concentrations corresponding to significant changes in LiNbO3〈Zn〉 crystallization conditions.

Structure and Optical Homogeneity of LiNbO 3 〈Mg〉 Crystals Grown from Different Charges

This paper reports a comparative study of the homogeneity of LiNbO3〈Mg〉 (≥5 mol % Mg) crystals grown from a charge synthesized using Nb2O5〈Mg〉 prepared through homogeneous magnesium doping of a reextract in the Nb2O5 extraction step, and LiNbO3〈Mg〉 crystals prepared through direct doping of a growth charge. The LiNbO3〈Mg〉 crystals were characterized by optical microscopy and Raman spectroscopy. The results demonstrate that the LiNbO3〈Mg〉 crystals prepared using homogeneous doping are more structurally uniform.

Effects of nonstoichiometry and doping on the curie temperature and defect structure of lithium niobate

LiNbO3 crystals doped with Gd, Zn, Cu, and Er to various levels were grown by the Czochralski technique. The structural parameters, Curie temperature, and density of the LiNbO3 crystals were determined as a function of composition. With increasing Gd content, thea parameter of the hexagonal cell increases, c remains constant within the experimental error, density increases, and Tc gradually decreases. The defect structure and properties of LiNbO3 doped with Gd, Zn, Cu, Er, Mg, and Ta are contrasted with those of nominally undoped LiNbO3 crystals differing in Li/Nb ratio. The results suggest that the variation of the Curie temperature with composition is determined primarily by the position that the dopant cations occupy in the structure of lithium niobate.

Growth of large LiNbO3〈Mg〉 crystals

We have analyzed conditions for the growth of large (≥80 mm in diameter) LiNbO3〈Mg〉 crystals in a wide range of dopant concentrations in the melt (2.9–5.8 mol % MgO). We have established conditions for the growth of large LiNbO3〈Mg〉 crystals uniform in doping level from melts containing magnesium concentrations above a certain threshold (Cmelt 5.0–5.8 mol % MgO) and optimized the high-temperature electrodiffusion annealing process, which allowed us to obtain single-domain, microstructurally homogeneous, large LiNbO3〈Mg〉 crystals containing 4.9–5.15 mol % magnesium.

Effect of the method used to prepare solid precursors Nb2O5:Mg on the characteristics of LiNbO3:Mg crystals produced on their basis

We investigated how the type of an extraction system affects the characteristics of precursors Nb2O5:Mg produced at the stage of extraction processing of niobium-containing HF-H2SO4 and HF-HCl solutions with an extractant comprising a mixture of dimethylamides of carboxylic acids of the C10–C13 fraction and 1-octanol in Escaid diluent. We also studied the optical properties of homogeneously doped crystals LiNbO3:Mg grown from a batch synthesized with the use of pentoxide Nb2O5:Mg obtained from various extraction systems. On Z-cut LiNbO3:Mg crystal wafers, such mechanical characteristics as Young’s modulus and microgravity were measured.

Spontaneous unipolarity and anomalies of the dielectric and piezoelectric properties and electrical conductivity of initially heavily doped polydomain LiNbO3: Zn crystals

A significant spontaneous unipolarity in initially polydomain LiNbO3: Zn crystals doped in the range of “threshold” impurity concentrations (∼4.5–4.7 mol %) has been revealed from high-temperature measurements and after high-temperature annealing under short circuit conditions. The effect of strong increase in the spontaneous unipolarity is accompanied by a pronounced low-frequency dielectric dispersion and abrupt anomalies in the temperature dependences of the electrical conductivity and dielectric permittivity. The piezoelectric coefficient d333 increases to nearly maximum values available in the reference literature for nominally pure single-domain LiNbO3 crystals.

Raman spectra of crystals LiNbO3:Zn(4.5), LiNbO3:Mg:Fe(5.01, 0.005), LiNbO3:Mg(5.1), and LiNbO3:Mg(5.3 mol %)

We have investigated the Raman spectra of strongly doped crystals that were grown from batches of different genesis. The LiNbO3:Mg(5.3 mol %) and LiNbO3:Mg:Fe(5.01, 0.005 mol %) crystals were obtained using methods of homogeneous doping and the LiNbO3:Mg(5.1 mol %) crystal was obtained using a solid-phase master addition alloy, while the LiNbO3:Zn(4.5 mol %) crystal was grown using direct doping. In the Y(ZZ){ie269-1} scattering geometry, we have revealed the occurrence of lines in the spectrum that correspond to fundamental vibrations of the A2 symmetry species, which are forbidden by the selection rules for the {ie269-2} space group. The occurrence of lines in the spectrum that correspond to fundamental vibrations of the A2 symmetry species has been explained by the existence of microstructures and clusters in strongly doped LiNbO3 crystals, which lead to significant local changes in the symmetry of the crystal.

Structure and Properties of Boron-Doped LiNbO 3 Single Crystals

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 of the LiNbO3〈B〉 crystals have been shown to approach those of the stoichiometric LiNbO3 and LiNbO3〈Zn〉 crystals.

Synthesis of homogeneously mg-doped lithium niobate batch and study of the effect of non-metal impurities on the properties of LiNbO3:Mg crystals

The preparation conditions for the homogeneously doped precursor Nb2O5:Mg for the synthesis of granulated lithium niobate batch was studied. The effect of non-metallic impurities in the Nb2O5:Mg precursors and the lithium niobate batch on the characteristics of the melt–crystal system and the physicochemical and optical characteristics of the LiNbO3:Mg crystals was established.

Effect of charge mixture preparation technology on the physicochemical and optical properties of LiNbO3:Mg crystals

LiNbO3:MgO crystals, representing important materials for nonlinear optics, laser optics, integrated optics, and optical electronics owing to their high resistance with respect to optical damage, are studied. The crystals of LiNbO3:MgO were grown from a granulated charge mixture of lithium niobate synthesized using homogeneously doped Nb2O5:Mg precursors of different origin. The effect of organic substances used in the technology of lithium niobate charge mixture on the properties of LiNbO3:MgO single crystals is studied. It is found that the physicochemical and optical characteristics of LiNbO3:MgO crystals grown from charge mixtures synthesized from Nb2O5:Mg precursors obtained using organic solvents and without them differ to a considerable extent. It is suggested that the difference in the properties of LiNbO3:MgО crystals of different origin is caused by change in the structure of the ion complexes in the melt owing to the presence of traces of organic impurities. Change in the structure of ion complexes in the melt leads to change in crystallization mechanisms and, accordingly, in the chemical composition and the properties of LiNbO3:MgO crystals. Furthermore, it is shown that the use of homogeneous doping methods as opposed to the method of direct doping provides the distribution coefficient Keef > 1. That is, the method of homogeneous doping allows one to introduce a substantially greater concentration of an impurity element in the LiNbO3:MgO crystal compared with the direct method for doping the charge mixture at the same impurity concentration in the starting material.