As-substituted Tl2–xAsxBa2CaCu2O8+δ (Tl-2212) high-temperature superconductor was synthesized using a two-step method. In the first step, the Ba2CaCu2Oy multiphase precursor was prepared via the in situ polymerization method, and in the second step, Tl and As were simultaneously introduced as dopants (x = 0.5–2.0 wt%). The final synthetic step was carried out in a closed quartz tube under an oxygen pressure of 2 atm. The non-substituted sample showed an onset superconducting transition temperature, Tc(onset), of 107 K. The sample doped with 1.5 wt% As showed the highest Tc(onset) ≈ 114.5 K. However, further substitution with 2.0 wt% As led to a decrease in the transition temperature. Notably, the sample dope with 0.5 wt% As displayed a significant enhancement in intergranular critical current densities, surpassing those of the As-free sample. Overall, the results showed that moderate doping with arsenic trioxide (As2O3, x = 0.5–1.5 wt%) enhances the onset critical superconducting transition temperature, while higher doping levels (1.0–2.0 wt%) adversely affect the intergranular critical current density.

The creep and mechanical stress relaxation in As–Se glasses at various temperatures were investigated experimentally, and the behavior of parameters that describe elastic properties and internal friction was analyzed within the framework of the classical standard models of solids and of the Burgers model. The theoretical basis for the description of viscoelastic phenomena in solids, in particular glassy materials, using the fractal Scott–Blair element is considered, and a mixed model incorporating of the Maxwell and Scott–Blair elements was proposed. A comparison of the correspondence between the experimental results and the parameters of the Burgers model and the mixed classical-fractal model was carried out. It was shown that the proposed mixed model takes into account the elastic and residual plastic deformation, as well as the power law dependence of the viscoelasticity.

The low symmetry of the crystals of the layered structure causes a clear spatial arrangement of associates of point defects. The generation of complexes of donor-acceptor-donor trimmers is the result of such a process. Crystals like CdI2 serve the ideal object for the justification of such associates creation. Peculiarities of the AX2 (CdI2) crystals causes the ordering of the local minimum of thermodynamic potentials at the sites occupied by cadmium cations. Model of donor-acceptor defects caused by mentioned above nonstoichiometric Cd inclusions is considered. The influence of the concentration of nonstoichiometric Cd inclusions on the electro-optical and photoelectric properties of CdI2 crystals is studied experimentally and theoretically using virtual crystal model and peculiarities of energy band due to different chemical bond in different directions.

The paper investigates the properties of electron and interface phonon states, and the influence of electron-interface-phonon interaction on the electron spectral characteristics in AlGaN/GaN/AlGaN nanostructures, as a key element of nanodevices. Using the Green’s function method at cryogenic temperatures, the mass operator was calculated. This made it possible to investigate the renormalized spectral characteristics of electron states due to interaction with all branches of interface phonons. We studied the partial contributions of individual phonon branches and configurational interactions to the shifts of the two lowest electron states. It has been established that the interaction with interface phonons at cryogenic temperatures leads to low-energy shifts of all electron states and to damping of only the excited states. The influence of the quantum well’s geometric parameters on the renormalization of the electron spectrum was also analyzed.

The normal and reverse indentation size effects for annealed and highly deformed Al, Al–Li alloy, Cu, and titanium VT1-0 were investigated. The normal indentation size effect (ISE) was revealed in all metals studied at large indentation depths. This behavior can only partially be described using the Nix and Gao model (NG) to interpret the depth-dependent hardness. The Feng and Nix correction to the NG model for small indentation depths works well for annealed coarse-grained (CG) metals. To explain the observed hardness dependence on the indentation depth, it is necessary to take into account the structure state of the surface layer. Grinding and mechanical polish of annealed fcc metals, such as aluminum, create a work-hardened layer that has higher hardness value compared to an electropolished sample as the load decreases and hence more pronounced ISE. Mechanical treatment of surfaces resulted in work-hardening of the thin layer in annealed CG metals and softening in naturally hard, ultrafine-grained, nano-crystalline, and hardening metals, changing the mechanical response of the metal at tension and contact deformation. In metals subjected to heavy plastic deformation, we first observed the reverse indentation size effect (RISE) phenomena where microhardness decreases with decreasing applied load.

A modified Monte Carlo method was developed that mimics phase transitions in atomic clusters and implemented to obtain, for the first time via computer modeling, size dependencies of argon cluster properties in the mesoscopic size range from 2000 to 12000 atoms and in a temperature range of 20–80 K. Thermodynamic functions were calculated and the equilibrium phase state was found for these temperatures. Two criteria, such as melting temperature and mean interatomic distance, show in accordance that cluster thermal properties become close to that of a macroscopic body at cluster size Ncl ≈ 10000 atoms. The proposed method allows one to avoid the exponential growth of the required number of Monte Carlo steps with cluster size, thus exponentially diminishing the required simulation time.

The article presents the results of an experimental study on the kinetics of cantilever deformation in the α-region of the α-PdHn alloy, conducted during successive hydrogen injections with the same concentration increase and different gas supply rates. It was established that each subsequent hydrogen injection leads to an increase in the time to achieve maximum bending and its duration, which is associated with the accumulation of hydrogen in the crystal lattice and the growth of internal concentration stresses. For the first time, a pronounced plateau effect was experimentally observed after achieving maximum bending, indicating the establishment of thermobaroelastic equilibrium between the processes of hydrogen penetration and the mechanical reaction of the material. Exponential relationships between the bending magnitude and the time to achieve it, as well as logarithmic relationships between the bending and the hydrogen supply rate, were established. The obtained patterns can be used to predict the behavior of palladium alloys in a hydrogen environment and to develop hydrogen concentration sensors.

The present numerical study is devoted to development and optimization of a metasurface-based sensor with graphene constituents for potential biosensing applications. A unit cell of the proposed metasurface consists of a thin flexible dielectric substrate layer with a centrally positioned graphene microstrip. As a result of numerical modeling of spectral properties of the metasurface by COMSOL Multiphysics software in terahertz range from 5 to 35 THz the absorption spectrum maxima (resonance modes) at f1 = 8.7 THz and f2 = 26.5 THz are revealed. Structural parameters of the developed metasurface with graphene microstrips have been tuned to achieve the optimal resonance properties. The following stages of the study demonstrate that placement of a layer of tested liquid sample [water or bovine serum albumin (BSA) solution] on the metasurface causes a low-frequency shift of the plasmonic resonance mode f1 chosen for biosensing measurements. This frequency shift, along with the change in the amplitude of the absorption peak, are highly sensitive to the refractive index of the tested liquid sample. The resonance behavior of the developed metasurface structure is governed by the excitation of localized plasmon resonance in the graphene elements and near-field electromagnetic coupling effect between the short edges of the graphene microstrips. Evaluation of the influence of dielectric substrate’s material on the sensitivity of the metasurface-based sensor to variations in BSA concentration indicates that Kapton substrate provides higher effectiveness compared with SiC substrate. The obtained results demonstrate the potential of the developed metasurface-based sensor with graphene microstrips for application as a sensing structure to determine proteins and other biomolecules in liquid samples.

The work analyzes the effect of a magnetic field B directed along the c axis (B || c) up to 9 T on the resistivity ρ(T), fluctuation conductivity (FLC) σ′(T) and pseudogap Δ*(T) in thin films of YBa2Cu3O7–δ with a critical temperature of the superconducting transition Tc = 88.8 K. In contrast to previous work (Low Temp. Phys. 51, 1061 (2025) [Fiz. Nyzk. Temp. 51, 1180 (2025)]), where the magnetic field was directed along the ab plane (B || ab), the influence of the field on the sample is stronger due to the contribution of both spin-orbit and Zeeman effects. As expected, the magnetic field does not affect ρ(T) in the normal state. However, at the superconducting (SC) transition, it sharply increases ρ(T), the width of the SC transition ΔTc, and the coherence length along the c axis, ξc(0), but at the same time reduces both Tc and the range of the SC fluctuations ΔTfl. The FLC reveals a transition at a characteristic temperature T0 from the three-dimensional Aslamazov–Larkin (3D–AL) theory near Tc to the two-dimensional Maki–Thompson (2D–MT) fluctuation theory. However, at B = 1 T, the 2D–MT contribution is completely suppressed, and above T0, σ′(T) is unexpectedly described by the 2D–AL fluctuation contribution, indicating the formation of a two-dimensional vortex lattice in the film under the action of a magnetic field. It was found that the BEC–BCS transition temperature, Tpair, which corresponds to the maximum of the Δ*(T) dependence, shifts to the region of lower temperatures with increasing B, and the maximum value of Δ*(Tpair) decreases in fields B > 5 T. It was found that with increasing field, the low-temperature maximum near T0 is smeared and disappears at B > 1 T. In addition, above the Ginzburg temperature TG, for B > 1 T, a minimum appears on Δ*(T) at Tmin, which becomes very pronounced with a subsequent increase in B. As a result, the overall value of Δ*(TG) decreases noticeably, most likely due to the pair-breaking effect. At the same time, ΔТfl and ξс(0) increase sharply by approximately 3 times with increasing B above 1 T. Our results confirm the possibility of the formation of a vortex state in YBa2Cu3O7–δ by a magnetic field and its evolution with increasing B.

This article describes the mechanism of changes in capacitance and resistance in magnetic tunnel junctions (MTJs) upon magnetization reversal of one of the electrodes and presents the results of measurements of the tunnel magnetic resistance and tunnel magnetic capacitance in MTJs Tb22-δCo5Fe73/Pr6O11/Tb19-δCo5Fe76 with perpendicular anisotropy electrodes and in MTJs Co80Fe20/Pr6O11/Co30Fe70, where the magnetic electrodes have uniaxial anisotropy in the plane. It shows that when the magnetic electrodes in the magnetic tunnel are magnetized, a strong magnetic field gradient appears in the barrier nonmagnetic layer, which causes a spatial redistribution of the concentration of spin-polarized electrons in the magnetic metal/insulator interface region and leads to the appearance of an uneven distribution of electric charge. Such a magnetically induced charge affects the dielectric characteristics of the barrier nanolayer and leads to a change in the resistance and capacitance of MTJs. Moreover, this effect is most pronounced in tunnel magnetic contacts with magnetic electrodes that have perpendicular anisotropy. The change in resistance during magnetization reversal of MTJs Tb22-δCo5Fe73/Pr6O11/Tb19-δCo5Fe76 reached 120% and in MTJs Co80Fe20/Pr6O11/Co30Fe70, it did not exceed 40%. The change in capacitance during magnetization reversal of MTJs Tb22-δCo5Fe73/Pr6O11/Tb19-δCo5Fe76 reached values of 110%, and the change in capacitance of MTJs Co80Fe20/Pr6O11/Co30Fe70 reached values of 45%. This work also presents a construction scheme of a data carrier based on MTJs and describes the principle of recording and reading information from such a carrier.