S. M. Masloboeva

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.

Synthesis and properties of homogeneously doped Nb2O5〈Dy〉 and a LiNbO3〈Dy〉growth charge

We have studied conditions for the synthesis of niobium pentoxide and a lithium niobate growth charge doped with dysprosium, which was added to niobium hydroxide obtained through extraction processing of rare-metal-containing raw materials. The phase composition of Nb2O5〈Dy〉 precursors was determined by X-ray diffraction and IR spectroscopy. Using inductively coupled plasma mass spectrometry in combination with a laser ablation sampling system, we examined the Dy dopant profile in Nb2O5 powder samples and the LiNbO3 growth charge. The Nb2O5 precursors and the growth charge synthesized using them were shown to be chemically uniform in composition. The present results are of importance for the growth of defect-free lithium niobate single crystals of optical quality, highly uniform in composition, with a predetermined doping level.

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.

Synthesis of Nb2O5〈B〉 solid precursors and LiNbO3〈B〉 batches and their phase compositions

A process has been developed for preparing boron-doped niobium pentoxides Nb2O5〈B〉 to be used as precursors in the sysnthesis of nithium biobate batches LiNbO3〈B〉 having tailored dopant concentrations. Solutions of various origins were used to isolate Nb2O5〈B〉. A method has been advanced to account for boron loss as volatile compounds upon the heat treatment of niobium hydroxide in order to determine the boron amount to be added to niobium hydroxide in the form of H3BO3. The boron concentration in LiNbO3〈B〉 during lithium niobate synthesis is shown to be independent of the origin of the Nb2O5〈B〉 precursor with the same as-batch boron concentration. The phase compositions of Nb2O5〈B〉 and LiNbO3〈B〉 have been characterized by X-ray powder diffraction and IR spectroscopy and boron concentrations have been determined for the synthesis of single-phase lithium niobate batches for use in the production of optically uniform single crystals and pore-free piezoelectric ceramics.

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.

New Approach to the Preparation of Doped Lithium Niobate Batches for Single Crystal Growth

Technological approaches have been developed to the preparation of single-phase lithium niobate batches doped with magnesium, zinc, iron, and rarer-earth elements (TR = La, Pr, Nd, Sm, Gd, Dy, or Er) from high-purity niobium-containing solutions to avoid niobium pentoxide separation, its mixing with lithium carbonate, and LiNbO3 preparation from this mixture by a solid-phase reaction. Two process flowsheets have been proposed, being applicable over the entire ranges of the studied dopant concentrations. Optimal parameters for preparing single-phase LiNbO3 batches of tailored compositions have been determined. The batches prepared by the developed technology are intended for growing doped optical-quality lithium niobate single crystals.

Synthesis and investigation of homogeneously doped precursor Ta2O5〈Sm〉 and charge of composition LiTaO3〈Sm〉

For growing single crystals of lithium tantalate of optical quality with high homogeneity of their composition and desired concentration of dopant of samarium a method for producing a solid precursor Ta2O5〈Sm〉 and homogeneously doped charge LiTaO3〈Sm〉 of a congruent composition was developed. X-ray diffraction analysis and IR spectroscopy were used to study the phase composition of Ta2O5〈Sm〉 and LiTaO3〈Sm〉. Conditions for preparation of the monophasic charge LiTaO3〈Sm〉 were determined: (Sm concentration in Ta2O5 ≤ 1.5 wt %, the molar ratio [Li2O]/[Ta2O5] = 0.941, synthesis temperature 1200°C). By mass spectrometry with inductively coupled plasma and sampling by laser ablation a distribution of the dopant of samarium in Ta2O5〈Sm〉 and LiTaO3〈Sm〉 was examined and the chemical homogeneity of the synthesized products was confirmed.

Preparation and phase composition of Ta2O5:Zn alloys having low Zn2+ concentrations

Methods were developed for preparing Ta2O5:Zn alloys containing less than 3 wt % Zn2+ for the purpose of using them further in preparing lithium tantalate batches and growing from them single crystals having improved properties. A method where zinc is doped directly into a tantalum-containing back-extract followed by precipitation of tantalum and zinc hydroxides with ammonia is confined to a Zn2+ concentration of 1.7 wt % in Ta2O5; at higher concentrations, Zn2+ forms soluble ammine complexes. A method where Zn2+ is extracted by high-purity tantalum hydroxide is applicable within the range of Zn2+ concentrations studied. Optimal conditions were found for preparing Ta2O5:Zn2+ alloys of various compositions. X-ray powder diffraction and IR spectroscopy were used to study the phase composition of the alloys synthesized, and Zn2+ concentrations were determined at which a ZnTa2O6 phase was formed along with the major Ta2O5 phase.

Study of the layering process in extraction systems for optimization of the technology of rare earth elements production

Effect of the contents of non-rare-earth admixtures, in particular calcium, and of the concentration of nitric acid in initial solutions on the rate of layering emulsions was studied the model extraction systems tributyl phosphate, nitric acid REE solutions. The opportunity to reduce areas of settling chambers by a factor of 4–5 at the subsequent steps of the separation and production of individual rare-earth elements.

Synthesis and research of phase composition of alloys Nb2O5: Fe3+ and Ta2O5: Fe3+

The conditions were studied for the synthesis of niobium and tantalum pentoxide containing iron impurity introduced into the strip liquor after extraction separation of niobium and tantalum and subsequent precipitation of metal hydroxides with ammonia. A phase composition of the synthesized alloys was examined by X-ray diffraction and infrared spectroscopy.