Vol 88, No 5 (2024)

The microstructure features and complex electromechanical parameters of porous piezoelectric ceramics based on the lead zirconate-titanate system with different relative porosities and pore sizes were studied. It was revealed that the microstructural features of porous piezoceramics define the character of the porosity dependences of electromechanical properties of porous piezoelectric ceramics.

The influence of silicon dioxide on the structure and dielectric properties of ceramic barium titanate was studied. The obtained results show that Si in concentrations up to 1 mol. % enters to the BaTiO₃ lattice, forming the BaTi_1-xSi_xO₃ solid solution. Doping barium titanate with silicon leads to a decrease in the size of the crystal cell, a slight diffuseness of the ferroelectric phase transition, a decrease in its temperature and the appearance of signs of a relaxer ferroelectric.

Polycrystalline thin films of bismuth-strontium tantalum Sr_yBi_2+xTa₂O₉ with different molar ratio Sr:Bi:Ta were obtained by sol-gel method. The formation of a phase with a perovskite structure has been established. Phase transitions have been confirmed by dielectric spectroscopy. In the mode of polarization switching spectroscopy, remnant piezoelectric hysteresis loops were obtained, which confirms the ferroelectric nature of the synthesized Sr_yBi_2+xTa₂O₉ films.

For ferroelectrics lead zirconate titanate and barium titanate, an exponential dependence of the dielectric constant on temperature is shown, provided that the Curie–Weiss law is satisfied. The temperature of equality of ferroelectric dielectric constants for activation processes caused by the interaction of domain walls with point defects, as well as the corresponding activation energies, have been determined.

Crystals of gadolinium-aluminum-gallium garnets with the following charge compositions: Gd₃Al_xGa_5-xO₁₂ (x = 1—3) and Gd₃Al₂Ga₃O₁₂:Ce³⁺ were grown The influence of high-temperature annealing in air on the optical properties of these crystals has been established. It was shown that annealing does not affect the oxidation state of cerium. Using X-ray fluorescence analysis, a gallium deficiency was established in all the studied crystals.

The results of molecular dynamics and atomistic simulations demonstrate segregation of Pd atoms to the surface of binary Pt-Pd nanoparticles and the surface segregation of Cr in Ni-Cr nanoparticles. At the same time, molecular dynamics results predict a transition from the surface segregation of Cr to the surface segregation of Ni at low Cr contents in Ni-Cr nanoparticles.

The values of microhardness of samples of single crystals of paratellurite differing from each other in growth conditions and structural quality were measured. For the plane (110), these values lie in the range — 300—470 kG/mm². It has been determined that mechanical stresses in paratellurite can lead to significant deviations of values of microhardness from average values.

A new scheme for controlling the position and intensity of unpolarized radiation, including at several wavelengths, has been developed. A feature of the optical scheme is the use of two–coordinate acousto-optic deflectors, each of which works with linearly polarized radiation — horizontal and vertical. A polarizing plate is used to separate the initial unpolarized laser radiation. Estimates of optical losses when using acousto-optic systems are given.

Suggested a method to reconstruct the Raman scattering tensor by studying the angular dependences of Raman line intensities in tiny unoriented microcrystals. The method was verified on well-known calomel Hg₂Cl₂ model crystals. The spectral line phase-indicators in the Raman spectra reveal different symmetry types of DUT-8 (Ni) metal-organic framework crystals in the open pores and closed pores phases. A technique can be used to reconstruct the Raman scattering tensor of any unoriented crystalline samples.

Within the framework of the phenomenological approach, we have obtained an inhomogeneous electric polarization associated with the appearance of an inhomogeneous magnetization distribution in the volume of small magnetic particles near the second-order phase transition from paramagnetic to ferromagnetic state. The temperature area of the existence of such inhomogeneous states for spherical shape particles of different sizes is determined. The change in the local electric polarization of small magnetic particles in an external magnetic field is considered.

The results of magnetization curves analysis of Y₂(Fe_xCo_1−x)₁₇ compounds, measured in 300—923 K temperature interval along easy and hard magnetization direction, were represented. Magnetocrystalline anisotropy constants K_1,2 of the samples were calculated. Temperature and compositional dependence of anisotropy constants K_1,2 and saturation magnetization M_s were discussed. There is an increase of first anisotropy constant K₁ value with the increase of relative samples iron concentration with maximum value of 5.1∙10⁵ J·m^-3 in x = 0.29 point, correspond to the middle of the easy-axis interval.

The behavior of the (Gd, Zr)(CoCuFe)_Z alloys samples in magnetic fields oriented at different angles to their easy magnetization axis has been studied. The angular dependences of magnetization and coercivity were constructed. The hysteresis loops of the two main structural components of the samples were constructed based on images of the domain structure in demagnetizing fields. An analysis of the obtained results was carried out under assumption of the mixed mechanism of hysteresis in these alloy family.