Dmytro Sugak

In the current work, nanocrystalline powders with different compositions, namely Li_0.98Pr_0.02NbO₃, Li_0.93Pr_0.02Mg_0.05NbO₃ and Li_0.98Pr_0.02TaO₃ were synthesized for the first time using the method of high-energy ball milling of the starting materials (Li₂CO₃, Nb₂O₅, Ta₂O₅, MgO, Pr₆O₁₁), followed by high-temperature annealing. XRD data analysis confirmed the absence of parasitic phases in the obtained nanocrystalline compounds. The estimated particle sizes ranged from 20 to 80 nm. From the obtained nanopowders, ceramic samples were prepared using specially developed equipment, which allowed for pressing at elevated temperatures with a simultaneous application of a constant electric field. The obtained photoluminescence spectra exhibit characteristic features of Pr³⁺ ions in the crystal structure of LiNbO₃ and LiTaO₃ and are most efficiently excited by UV light. Samples pressed with an electric field application show higher intensity of photoluminescence. Investigations of the temperature dependence of electrical conductivity of the Li_0.98Pr_0.02NbO₃ sample, pressed with the application of an electric field, indicate that the conductivity mechanism is similar to that of LiNbO₃ single crystals and, at high temperatures, is attributed to the lithium conduction mechanism.

The changes in the optical, structural, mechanical properties, and chemical composition of Y₃Fe₅O₁₂/Gd₃Ga₅O₁₂ (YIG/GGG) single crystal structures grown by liquid phase epitaxy, particularly at the interface between the film (Y₃Fe₅O₁₂) and the substrate (Gd₃Ga₅O₁₂), are studied. Different complementary techniques, including optical microscopy, local spectrophotometry, electron probe microanalysis, micro‐Raman spectroscopy, and nanohardness analysis are used. The main finding of the study is an experimental approach, in which the probe of the measuring device (light beam, electron beam, nanoindenter) is directed to the surface of the studied sample in a direction perpendicular to the direction of structure growth, and the surface is scanned along this direction. It allows to obtain the profiles of changes in refractive properties, nanohardness, optical absorption, chemical composition, and intensity of phonon spectrum bands at the transition from the GGG to YIG. It is established that the lengths of the scanning intervals, at which the changes of various properties of a specimen occur, differ significantly. The obtained results are affected by the size of the probes and by the sensitivities of both the particular measuring method and the particular physical property of the material to changes in the chemical composition and crystalline structure of the sample.

Nanocrystalline compounds LiNb_1−xTa_xO₃ of various compositions (x = 0, 0.25, 0.5, 0.75, 1) were synthesized by high-energy ball milling of the initial materials (Li₂CO₃, Nb₂O₅, Ta₂O₅) and subsequent high-temperature annealing of the resulting powders. Data on the phase composition of the nanopowders were obtained by X-ray diffraction methods, and the dependence of the structural parameters of LiNb_1−xTa_xO₃ compounds on the value of x was established. As a result of the experiments, the optimal parameters of the milling and annealing runs were determined, which made it possible to obtain single-phase compounds. The Raman scattering spectra of LiNb_1−xTa_xO₃ compounds (x = 0, 0.25, 0.5, 0.75, 1) have been investigated. Preliminary experiments have been carried out to study the temperature dependences of their electrical conductivity.

Doping ions and OH⁻ groups absorption bands spatial profiles were investigated for the case of congruent LiNbO₃ single crystal grown by Czochralski technique. Doping was performed after the crystal growth by diffusion at elevated temperatures. The changes of the optical absorption caused by diffusion of Cu were measured in the Y crystallographic direction. It is shown, that the spatial distributions of the intensity and the position of OH⁻ absorption band correlates with the distribution of copper ions