Vol 83, No 9 (2019)

Phenomenological models of phase transitions for two- and three-component order parameters are constructed by means of catastrophe theory using equivariant vector fields that consider the symmetry of the thermodynamic system. The models are classified according to the number of control parameters, depending on external thermodynamic conditions. Phase diagrams of some models are constructed and theoretical temperature dependences of their thermal properties are calculated. A comparison of theoretical and experimental data show a satisfactory match in quality.

It is shown in terms of the phenomenological Landau theory of second-order phase transitions that a phase transition to a nonuniform domain-like phase is possible in a thin ferroelastic rod. The wave vector of the nonuniform structure is determined and the conditions for the existence of the latter are established, depending on the geometric dimensions of the ferroelastic rod, its elastic properties, and the properties of the surface.

Coefficients of the expansion of electrical energy \({{W}_{c}}\) in the ferroelectric phase near phase transition temperature \({{T}_{c}}\) are determined from an even power series according to polarization \({{P}_{c}}\) by studying the dynamics of repolarization in A₂BX₄ group crystals according to the Landau–Ginzburg–Devonshire theory. Experimental results are compared to the theoretical concepts of the Landau–Ginzburg–Devonshire theory describing dependences \({{W}_{c}}({{P}_{c}})\) in static.

The temperature dependences of the dielectric constant and the intensity of the third harmonics are studied at temperatures of 100–470 K for barium titanate, strontium titanate, and a 0.5BaTiO₃–0.5SrTiO₃ blended nanocomposite with an average crystallite size of around 100 nm. Magnetic hysteresis loops are obtained for BaTiO₃ and SrTiO₃ samples whose room-temperature spontaneous magnetizations are comparable in value. The effect thermal treatment has on the magnetic properties of nanocrystalline strontium titanate is discussed. Their spontaneous magnetization is shown to decline as a result of thermal treatment.

The processes of low-frequency and infra-low-frequency polarization in solid solutions (1 ‒ х) Ba_0.95Pb_0.05TiO₃ + хСо₂О₃ (x = 0; 0.1; 0.3; 0.5; 1; 2 wt %) prepared using conventional ceramic technology are studied at a wide range of temperatures. It is shown that adding cobalt (Co) substantially alters the thermal anomalies of the dielectric properties of samples and shifts the temperature of the ferroelectric phase transition. Data on the dielectric response in the samples are compared to the behavior of the elastic properties of ceramics at different contents of impurities. It is established that the disordering of the ceramic structure increases as Co is added. The domain component, which determines the main contribution from low-frequency polarization, is greatly reduced, and the nature of the dielectric non-linearity of the material is determined by inducing a macroscopic polar state from the microscopic state (the accumulation of polar nanodomains and phase boundaries).

Localized electronic states in a planar semiconductor heterostructure with energies in the range of continuum spectrum are considered within one-band approximation. The reason for the confinement is shown to be quite general and not sensitive to details of theoretical description. To discover domains of the Brillouin zone that could host over-barrier confined states a criterion is proposed based on comparing bulk electron energy spectra of the semiconductors which the heterostructure is composed of.

The boundary problem for the eigenvalues of the electroelasticity equations describing the oscillations of a cylindrical resonator of a hemispherical resonator gyroscope is solved by finite element means. The first ten resonator frequencies are determined under different boundary conditions where PZT-4 ceramics are used as piezoelectric transducers for the buildup and pickup of signals.

Multilayered [(Co₄₀Fe₄₀B₂₀)₃₄(SiO₂)₆₆/ZnO]₁₁₂, [(Co₄₀Fe₄₀B₂₀)₃₄(SiO₂)₆₆/SnO₂]₃₂, and [(Co₄₀Fe₄₀B₂₀)₃₄(SiO₂)₆₆/In₂O₃]₉₂ films with layers 1 nm thick are obtained via the ion-beam sputtering of two targets onto a rotating substrate. Their phase transformations are studied during the thermal treatment of films. Compounds with boron form in films with ZnO and In₂O₃ buffer layers (Co₂FeO₂(BO₃) and InBO₃, respectively). The composition of these compounds is found to depend on the semiconductor that is used and the ratio of layer thickness.

The destruction of vulcanized butyl rubbers induced by ionizing radiation is described mathematically. A way of estimating the effect a dose of radiation has on a change in the viscoelastic properties of a polymer is proposed that would allow polymer materials with predetermined viscoelastic properties to be obtained, along with ensuring rational use of energy resources and the duration of radiation treatment of materials.

Properties of the states of yrast bands in even Ba isotopes are studied on the basis of the boson representation of fermion operators. The parameters of the boson Hamiltonian and the interaction between collective quadrupole bosons, positive parity bosons, and spins \({{J}^{\pi }}\) from \({{0}^{ + }}\) to \({{10}^{ + }}\) are calculated microscopically. This approach describes band crossing in the yrast bands and reproduces their energies and \(B(E2)\) within these bands up to \({{I}^{\pi }} = {{18}^{ + }}.\)

A way of calculating the angular distribution of changes in the energy of optical radiation generated by high-energy electrons passing through a solid transparent body is proposed that allows for the contribution from secondary electrons. The values are found of the angles at which peaks in optical radiation are observed when electrons pass through mica and glass.

The increased luminosity of modern accelerators allows the scope of research to be expanded in experiments on fixed targets in high-energy physics. New prospects are thus opening up for studying so-called cumulative processes. These can be associated with the formation of the multi-quark configurations within nuclei (so-called fluctons, which are dense clots of cold quark–gluon plasma). Their detection and study in hadron collisions is possible by registering secondary particles in the region kinematically forbidden for reactions on free nucleons. It is of particular interest to study correlations between the production of cumulative particles and particles that contain strange quarks and heavy flavors, an increase in the yield of which is expected in cumulative processes. The concept of a new detector for registering particles in hadron–hadron collisions in cumulative processes is presented, along with the corresponding results from their modeling.

We find the influence of three nucleon and four nucleon forces on the nucleon characteristics in symmetric nuclear matter. We employ the finite density QCD sum rules method. The matter is considered as a system of “pion dressed” nucleons. This means that single particle nucleon states include the one pion exchanges as well as the iterated one pion exchanges. The approach provides strong hierarchy of many body forces.

A spinor theory with automatic second quantization and no need for normalizing operators is constructed, based on a superalgebraic representation of spinors and Dirac matrices. The creation and annihilation operators of spinors are constructed using integrals of Grassmann variable densities in the momentum space and derivatives with respect to them. Formulas for superalgebraic bilinear covariants, and fermionic Lagrangian, and Noether currents are derived.

The energy spectra of protons and α particles are obtained for a wide range of angles in reactions between α particles with an energy of 29 MeV and ²⁷Al and ⁵⁹Co nuclei. The contributions from different mechanisms that shape the inclusive proton and α-particle spectra of the studied reactions are determined by analyzing the experimental data with the PRECO-2006 code. The experimental results are added to the bank of data needed for the development of advanced nuclear technologies.