Journal of V. N. Karazin Kharkiv National University. Series Physics

Features of the crystal structure and influence of long-term exposure in the air atmosphere on electrical transport of HTSC-compounds of system 1-2-3 (review)

Thu, 30 Nov 2023 00:00:00 +0000

The problem of the influence of a defect ensemble and long-term exposure in an air atmosphere on various mechanisms of electrical transport of HTSC compounds Re₁Ba₂Cu₃O_7-δ (Re = Y or other rare earth ion) is considered. The features of the crystal structure and the influence of structural defects of various morphologies on the electrical conductivity of these compounds in the normal, pseudogap, and superconducting states are discussed. A review of experimental data obtained from studies of the effect of long-term aging in air on various mechanisms of electrical transport of Re₁Ba₂Cu₃O_7-δ compounds of various compositions and technological backgrounds is carried out. The effect of long aging on stability of the oxygen subsystem and the electrical resistance of pure and aluminum-doped YBa₂Cu₃O_7-δ single crystals with a given topology of planar defects have been studied. Various theoretical models are discussed on the effect of long-term exposure in an air atmosphere on the electrical conductivity of HTSC compounds of the 1-2-3 system.

Features of plasmonic enhancement of luminescence of molecular aggregates of cyanine dyes

Thu, 30 Nov 2023 00:00:00 +0000

The article examines the effect of plasmon resonance of gold nanoparticles on the luminescent properties of molecular aggregates (J-aggregates) of two cyanine dyes, PIC and TDBC. It is shown that the luminescence enhancement of J-aggregates due to the exciton-plasmon interaction occurs in a very similar manner for both types of aggregates, namely: the largest enhancement factor is achieved at a distance between J-aggregates and nanoparticles of 15-20 nm, while the exciton delocalization length increases and increasing their lifetime, as well as suppressing the process of exciton self-trapping. However, these effects are more pronounced for PIC J-aggregates than for TDBC J-aggregates, despite the latter exhibiting better excitonic characteristics. It is proposed that the main factor of the detected discrepancies is the different structure of the exciton bands for J-aggregates and, accordingly, the different degree of overlap of their absorption bands with the plasmon resonance band of gold nanoparticles.

Functional characteristics of hydroxyapatite sintered at high temperatures

Thu, 30 Nov 2023 00:00:00 +0000

The functional characteristics of hydroxyapatite, which has carbonate impurities inside the hydroxyapatite crystal lattice after sintering in the temperature interval from room temperature to 1400°C have been studied. It has been shown, that carbonate impurities are present in hydroxyapatite up to 1000°C. Hydroxyapatite has a mixed AB - type of carbonate substitution. It has been shown, that all samples after the heating and sintering in the temperature interval from room to 1400°C contain single phase hydroxyapatite. The samples have density greater than 95% of the theoretical for hydroxyapatite at the temperature of 1200°C. The active shrinkage of the samples starts at temperature near 700°C and reaches the maximum value at 1280°C. The same tendency was demonstrated by the dependence of Vickers microhardness on sintered temperature. The maximum Vickers microhardness of 5.5 GPa was obtained in this work on the samples of hydroxyapatite after sintering at the temperature of 1100°C. The mechanisms of the hydroxyapatite sintering at 1150°C have been studied. It has been shown, that the diffusion during the sintering of the samples is realized by the surface diffusion mechanism, as well as through the interface grain boundaries in the polycrystalline hydroxyapatite. The microstructure of the hydroxyapatite particles after heating at high temperatures was studied. It has been shown, that at the initial stage of the sintering of hydroxyapatite, active mass transfer take place, which at the temperature of 1000°C leads to the sintering of the particles with neck formations between them. The Arenerus plot of the size of hydroxyapatite particles as a function of the heating temperature was obtained. The activation energy for diffusion processes in the particles at different temperatures was calculated. The obtained values were 36, 83, 5.11 and 11.28 kcal/mol at different intervals for the heating of hydroxyapatite.

Mechanical behavior and mechanisms of superplastic deformation of aluminum alloys exhibiting the effect of structural superplasticity in solid and in solid−liquid states

Thu, 30 Nov 2023 00:00:00 +0000

The article presents the results of research aimed at summarizing experimental data on the mechanical behavior, structural state and mechanisms of superplastic deformation of aluminum alloys Al-4 wt.% Ge, Al-4.1 wt.% Cu-0,5 wt.% Zr, 1420T, 1933. It is revealed that the initial microstructure of Al-4 wt.% Ge alloy samples is coarse-grained. Initial microstructure of 1420Т and 1933 alloy samples is bimodal. The study of characteristic types of samples microstructure deformed under the optimal conditions showed that the average grain size d_av in samples of Al-4.1 wt.% Cu-0.5 wt.% Zr and 1420T alloys increases slightly. It is revealed that in the course of superplastic deformation of Al-4 wt.% Ge and 1933 alloy samples, recrystallization takes place intensively, it leads to an increase in the initial grain sizes. Accumulation of cavities in the samples of all studied alloys during superplastic flow is observed. In the samples of alloys 1420T and 1933 during superplastic deformation, structural changes occur, which are probably associated with local melting of the alloys. The viscous flow of the metastable liquid-solid phase localized at the grain boundaries leads to the formation of fibrous structures in cavities and cracks. The study of the deformation relief of the samples gives grounds for asserting that their superplastic deformation takes place due to the cooperative development of deformation and accommodation mechanisms, namely grain boundary sliding, intragranular dislocation sliding and diffusion creep. The contribution of grain boundary sliding to the overall deformation of the samples was analyzed, as well as the likely influence of liquid phase inclusions on the mechanism of superplastic deformation of samples that exhibit the effect of structural superplasticity in the solid-liquid state.

Means and methods of conducting educational research at the general practicum in physics

Thu, 30 Nov 2023 00:00:00 +0000

The work presents the result of modernization of the equipment and methods of performing the work of the general physics laboratory practice. Modernization was carried out with the aim of giving the work of the workshop elements of research activity. Using the example of thematically related laboratory works from the section "Electricity and Magnetism", it is shown that the combination of several laboratory works into one study of the electrophysical properties of semiconductor materials provides an opportunity to gain deeper knowledge about the object of research and contributes to the development of research activity skills of physics students. The work investigated semiconductor diodes manufactured using different technologies: Schottky diode MBR2045, high-voltage p – i – n diode STTH6012 and diode with p – n junction D92 – 02. The study consisted of studying volt-ampere, volt-farad characteristics and temperature dependences of the reverse current of each of the specified products. The measurement results were processed using modern theoretical models of semiconductors. The equipment and skills acquired by students during the performance of such complex laboratory work can be used in research work if there are appropriate tasks.

Nobel Prize in Physics 2023

Thu, 30 Nov 2023 00:00:00 +0000

The laureates of the 2023 Nobel Prize in Physics are three researchers: Pierre Agostini (The Ohio State University, USA), Ferenc Krausz (Max Planck Institute of Quantum Optics, Garching and Ludwig-Maximilians-Universität München, Germany), and Anne L'Huillier (Lund University, Sweden). The prize was awarded for developing experimental methods that allow the generation of extremely short (attosecond) laser light pulses to study the dynamics of electrons in matter. The paper presents information about the scientific achievements of this year's Nobel laureates, which "give humanity new tools for exploring the world of electrons inside atoms and molecules." The paper describes the fundamental physical experiments that launched the new scientific field of attosecond physics. With its development, world science has gained many opportunities to study various fundamental physical processes and phenomena, as well as to create cutting-edge technologies, a brief overview of which is provided in the paper. A description of the new physical phenomenon discovered by the laureates, which was called electron-ion recollision, is given.

In memory of Valerian Ivanovich Startsev (1913 – 1988)

Wed, 17 Apr 2024 15:40:31 +0000

The article is devoted to the 110th anniversary of the birth of Valerian Ivanovych Startsev, Doctor of Physical and Mathematical Sciences, Professor, Honored Worker of Science and Technology of the Ukrainian SSR, an outstanding scientist in the field of crystal physics, physics of strength and plasticity, a well-known organizer of science and education in Kharkiv. Information about his scientific, scientific-organizational, scientific-pedagogical activities is presented. A brief overview of the fundamental and applied research conducted under the leadership and with the direct participation of V. I. Startsev is given. The results of these studies were included in the fund of ideas of modern science about the strength and plasticity of solids, stimulated the development of the physical theory of plasticity and dislocation physics.