Bystrenko O. Formation of ordered structures in condensed systems.

The phenomena of structure formation in two classes of condensed systems - multiparticle systems with the dominant Coulomb interaction and eutectic systems are studied. In numerical Monte Carlo experiments, an explanation for a series of structural transitions between phases with alternating square (body-centered cubic) and hexagonal (face-centered cubic or hexagonal closely packed) symmetry observed in the experiments with strongly coupled planar ion systems in Penning traps has been given. On the basis of the Monte Carlo simulations, the general applicability of the nonlinear Poisson-Boltzmann theory was substantiated and the effects of charge asymmetry and nonlinearity in macro-charge shielding on the crystallization of Coulomb structures in charged colloids were studied. It is shown that the allowance for the nonlinear effects in the Poisson-Boltzmann theory, as well as Monte Carlo atomistic simulations, result in qualitative differences from the linear Debye-Hückel theory. As the coupling constant increases, the plasma charges condense on the surface of macroions, resulting in complete shielding in the limit of small macroions. On the basis of the model with the shielded Yukawa potential, it is shown that the influence of nonlinear effects leads to the existence of a threshold for the minimum charge asymmetry, below which crystallization of Coulomb structures in colloidal systems is impossible. The effect of charging by plasma currents on the shielding of macroparticles in nonequilibrium dusty plasmas in the presence of collisions is investigated, and the properties of the charge dispersion due to fluctuations are considered. In simulations by Brownian dynamics, the possibility of self-organization of vortex structures in nonequilibrium two-component magnetized Coulomb systems is shown. The properties of binary eutectic systems are studied in the framework of the phase field theory and by the method of molecular dynamics. The kinetics of the formation of ordered structures during the directed crystallization of boride-boride ceramics is studied. To study the processes of structure formation in eutectic systems on the basis of the phase field theory, a method of direct calculation of the free energy functional is proposed. The structural and thermodynamic properties of interphase interfaces associated with contact phenomena are studied. The possibility of the existence of equilibrium three-phase states near the eutectic point corresponding to the complete decay of a binary eutectic with a liquid interface is shown. The influence of the surface energy of interfaces on the phase diagram of binary eutectic systems is considered. In numerical experiments by the method of molecular dynamics, the kinetics of contact phenomena in the binary eutectic was studied. A method for analyzing crystal structures using strain-invariant structural functions based on the study of the topology of a network of chemical bonds is proposed. The kinetics of bonds during the destruction of icosahedral boron carbide under uniaxial loads is considered. The results obtained and the proposed methods can be used in theoretical studies of the phenomena of structure formation in condensed systems, in the development and improvement of technological processes for the production of ceramic composites and structured materials for optoelectronics; to improve plasma etching technologies and material processing.