V. V. Efremov

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.

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.

Mechanical properties of Nb2O5 and Ta2O5 prepared by different procedures

We have studied the mechanical properties of niobium pentoxide and tantalum pentoxide ceramics prepared by a conventional ceramic processing technique and by exposure to high-intensity light (HIL). The results demonstrate that, after HIL exposure in an optical furnace, the niobium pentoxide and tantalum pentoxide ceramics possess enhanced microhardness and improved mechanical properties (strength, fracture toughness, and brittle microstrength) owing to the formation of fractal micro- and nanostructures. With increasing exposure intensity, the strength of the Nb2O5 and Ta2O5 ceramics increases.

High-pressure synthesis, structure, and electrical properties of LixNa1 − xNbO3 solid solutions

The dielectric permittivity of LixNa1 − xNbO3 ferroelectric solid solutions prepared at high pressures has been measured as a function of temperature and frequency, and their structural properties have been studied. The results demonstrate that ceramics samples of the LixNa1 − xNbO3 (x = 0.17, 0.25) ferroelectric perovskite solid solutions exhibit superionic conduction at relatively low temperatures (T ≥ 400 K). In the temperature range of superionic conduction, we observe significant dielectric dispersion and anomalies in permittivity, corresponding to structural transformations of the high-pressure solid solutions.

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.

Dielectric properties and electrical conductivity of Li0.07Na0.93Ta0.1Nb0.9O3 and Li0.07Na0.93Ta0.111Nb0.889O3 ferroelectric solid solutions

The dielectric properties and electrical conductivity of the ferroelectric perovskite solid solutions Li0.07Na0.93Ta0.1Nb0.9O3 and Li0.07Na0.93Ta0.111Nb0.889O3 have been studied at temperatures from 290 to 700 K and frequencies from 25 Hz to 1 MHz. In this temperature range, the solid solutions undergo a first-order ferroelectric phase transition. Li0.07Na0.93Ta0.111Nb0.889O3 (prepared from coprecipitated Ta2yNb2(1 − y)O5 pentoxides) has a markedly lower Curie temperature (by ∼75 K) and higher ionic conductivity and high-frequency dielectric permittivity in comparison with Li0.07Na0.93Ta0.1Nb0.9O3 (prepared from a mechanical mixture of Ta2O5 and Nb2O5).

Structure and mechanical characteristics of ceramic Nb2O5 and Nb2(1 − y)Ta2yO5

The structure and mechanical characteristics of ceramic Nb2O5 and ceramic materials produced from coprecipitated Nb2(1 − y)Ta2yO5 pentoxides by a conventional ceramic processing technique and exposure to high-intensity light have been studied by scanning probe microscopy and Raman spectroscopy.

Dielectric properties and electrical conductivity of LixNa1−xTa0.1Nb0.9O3 ferroelectric solid solutions

We have studied the dielectric properties and electrical conductivity of LixNa1 − xTa0.1Nb0.9O3 (x = 0.03−0.135) ferroelectric solid solutions at temperatures from 290 to 700 K and frequencies from 25 to 106 Hz. The results demonstrate that charge transport in these materials is due to the Li+ ion and that their conductivity is dominated by volume ion transport. In the temperature range studied, the LixNa1 − xTa0.1Nb0.9O3 solid solutions undergo a first-order ferroelectric phase transition close to second order. Increasing the lithium content enhances features characteristic of second-order transitions.

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.