Bulletin of the Russian Academy of Sciences: Physics最新文献

Results of the synthesis and comprehensive characterization of rare earth oxide and fluoride nanoparticles Gd₂O₃:Eu³⁺, NaGdF₄:Eu³⁺, and NaGdF₄:Ce³⁺/Eu³⁺ are presented here. All nanoparticles were synthesized by thermal decomposition of organometallic precursors in high-boiling organic solvents. Structure, morphology and phase composition were studied using a wide range of physicochemical methods. It turned out that the introduction of Ce³⁺ with its allowed 4f–5d transitions promotes broadening of the excitation spectrum and significant enhancement of Eu³⁺ emission upon irradiation in the 254 nm region. Particular attention was paid to the study of energy transfer mechanisms, including the effect of Eu³⁺ ion concentration on the efficiency of cascade energy transfer along the Ce³⁺ → Gd³⁺ → Eu³⁺ channel. In order to assess the application potential, synthesized nanoparticles were encapsulated in a polyvinyl alcohol matrix and deposited on the surface of silicon solar cells. Resulting coating made it possible to increase the efficiency of photocurrent generation due to the spectral conversion of radiation from ultraviolet to visible spectral range.

For one-dimensional spin and pseudospin models that allow mapping to a Markov chain, the free energy of the system at a finite temperature can be expressed in terms of bond concentrations. Minimizing the free energy function makes it possible to obtain an exact solution of a statistical model. A dilute Ising chain with interacting impurities is considered as an example.

The results of calculations of the calcium cations substitution by iron in hydroxyapatite lattice using density functional theory methods are presented. Changes in the unit cell parameters and unit cell volume, the energy bands, and the magnetic properties with increasing number of substitutions in different calcium positions and for various charge of iron ions were analyzed in comparison with experimental data. The arisen magnetic properties of Fe-HAP are proportional to the amount of Fe introduced and energy levels Ei, filled by spin-up and spin-down electrons in different ratios.

We have studied experimentally the shape evolution of the interacting initial head-to-head (h2h) and tail-to-tail (t2t) charged domain walls (CDW) and growing isolated domain in the Y-cut LiNbO₃ plates. The wedge-like domains were created and grew by electric field application using biased tip of scanning probe microscope. Two h2h and one t2t initial CDWs have been produced during phase transition in the crystal with composition gradients created by in-diffusion and out-diffusion of Li. The formation and growth of cogged CDW has been revealed for domain interaction with t2t CDW in contrast to h2h CDW. Near the t2t CDW domain elongation is slowed down, while the widening of the domain part with neutral walls continues. The growth anisotropy leads to formation of the region with increased local tilt and formation of cogged CDW by generation of additional spikes. The obtained effects were considered in terms of kinetic approach to domain wall motion considering abnormal local field distribution in the vicinity of initial CDW with effectively screened depolarization field. The discovered effect can be considered for domain wall engineering thus paving the way for manufacturing of the nanoelectronics devices based on the CDWs.

The influence of conductive coating materials on the magnitude of short-circuit currents (SCC) in single-domain and polydomain Z-cut polar lithium niobate (LiNbO₃) crystals is investigated. The domain structure of the samples was determined by piezoresponse force microscopy (PFM) using a probe microscope. Indium and silver symmetrical (identical) coatings were used for the study. Temperature dependences of SCC were measured using a hardware complex with special software in the temperature range from room to 350°C at a rate of 2 deg/min in air without applying an external electric field. Even at room temperature the SCC are observed on all investigated samples. The direction of the SCC flow depends on the conductive coating material, and the domain structure influences the current magnitude during heating. The current flow was in the positive direction for In conductive coatings and in the negative direction for Ag conductive coatings. In the single-domain samples observed higher currents than those in polydomain ones. The surface of the conductive coatings before and after heating was investigated using an optical microscope. Significant changes in the structure and color of the conductive coatings are observed. The obtained data demonstrate a significant dependence of SCC on the type of domain structure and the material of conductive coatings, which is important to consider when developing stable piezoelectric devices operating in a wide temperature range.

Influence of density dependent hyperon–nucleon forces on characteristics of neutron stars is investigated. In particular, the role of the exponent γ, determining the dependence of interaction on the nucleon density, in the description of the matter of neutron stars is studied. It is also shown that the hyperon–nucleon forces proportional to the nucleon density and three-body hyperon–nucleon–nucleon forces can lead to qualitatively different results in neutron stars.

We provided an overview of the reports presented at the 75th International Conference “Nucleus-2025: Nuclear Physics, Elementary Particle Physics, and Nuclear Technologies,” which took place in St. Petersburg from July 1 to 6, 2025. The program covered nuclear structure, nuclear reactions, astrophysics, neutrino, high energy and particle physics, nuclear technologies. Emphasis was placed on medical, energy, radioecology and materials applications, demonstrating the growing interdisciplinary impact of nuclear science.

The influence of a uniform axial magnetic field on the drift of charged particles from the apex of a conical cathode in the surrounding gas is studied. A self-consistent analytical model is developed to describe this influence within the space-charge-limited current regime. Assuming the shape of the drift region to be conical, it is possible to determine the dependence of its opening angle on the electrode angle, the magnitude of the applied magnetic field, and the mobility of charge carriers.

The glow accompanying a self-sustained subnanosecond discharge in nitrogen in the pressure range from 4 to 15 atm was recorded using the streak method. Breakdown delay time and pulse breakdown voltage of the discharge gap were recorded oscillographically. The experiments were carried out in uniform and non-uniform average electric fields. In these cases, the macro geometry of the discharge gap did not provide an increase in the electric field to the value necessary for the implementation of the electron runaway mode according to the classical runaway criterion. It is shown that at the initial stage of development, the discharge has a volumetric shape, which later turns into a spark. The discharge contraction, as a rule, begins from the cathode and the anode almost simultaneously. The conducted modeling of the dynamics of ionization processes showed that at the stage of the volumetric column formation, a short-term increase in the electric field near the anode occurs. As a result, the ionization of gas in the anode region increases sharply, which initiates the development of a spark channel, including from the anode.

Numerical simulation of the shock wave propagation in the discharge chamber with the high-current discharge in high density hydrogen at initial pressure of 0.1–32 MPa under non-stationary energy release at current rise of rate of 10 GA/s was carried out by the finite-differences method. The source of the disturbance (shock wave) was a forming discharge channel in the interelectrode gap along the axis of the cylindrical chamber. The power disturbance of the source was given by the experimental power value in near-axis area.