Structure of conduction channels in superionic conductors: Crystallochemical modeling

The experimental and theoretical studies of the structure of conduction channels of superionic conductors are analyzed. A crystallochemical method of modeling the conduction channels is proposed in which they are treated as sets of polyhedron Vorono-Dirichlet sections outside of impenetrable spheres of the rigid sublattice. The allowance for both weak flexibility of the spheres and their mean-square displacements relative to the sublattice points yields a channel structure that “wraps” around the Vorono-Dirichlet polyhedron edges. Modeling the interionic potential for α-AgI with the help of equipotential surfaces suggests that the mobile-ion motion slips along the conduction channel walls. For α-AgI, the set of the equipotential surfaces specifies “the minimum energy trajectory” of transition into a superionic state, while the crystallochemical “wrapping” structure corresponds to a saddle point of a multidimensional potential surface. Symmetry selection rules are used for predicting mechanical trajectories as allowed oscillation modes for the tetrahedral and octahedral fragments of α-CuI.     

Nonlinear precession of magnetization in a ferrite-garnet film of the (100) type

The dynamics of stationary resonance precession during perpendicular biasing of a ferrite-garnet film of the (100) type in a wide range of resonance frequencies and amplitudes of an alternating field is studied on the basis of numerical solution of the magnetization motion equations. The influence of the crystallographic and growth anisotropy on the trajectories of precession motion is studied. A new type of symmetric precession trajectories is found and the states of dynamic bistability are revealed.     

Peculiarities of the diffraction contrast in plane-wave X-ray topographs of weakly deformed crystals in the bragg geometry

The regularities of the topographic contrast formation in weakly deformed nonabsorbing crystals in the Bragg geometry for the diffraction of a plane X-ray wave have been investigated by the method of Riemann functions. It is shown that in this case the extinction contrast has an interference character, alternates, and is proportional to the strain gradient rather than to the squared strain (like in the case of strong lattice distortions). The data of the analysis are compared with the results of a model numerical experiment. The possibility of implementing an X-ray-acoustic resonance in the Bragg geometry is shown.     

Bulk polaritons in a biaxial crystal at the interface with a perfect metal

The orientation of the plane where the tangential electric field component becomes zero is indicated for any plane bulk electromagnetic wave propagating in an infinite transparent medium of arbitrary anisotropy. Thus, the existence of this wave (bulk polariton) in this plane (interface with an ideal conductor) is ensured. The characteristics of such polaritons of two independent branches with coinciding wave normals (isonormal polaritons) or Poynting vector directions (isoray polaritons) are compared.     

Chaotic magnetization dynamics in single-crystal thin-film structures

The nonlinear dynamics of homogeneously precessing magnetization in perpendicularly magnetized single-crystal films has been investigated in a wide range of ac field frequencies on the basis of a numerical solution to the Landau-Lifshitz equation and construction of the spectrum of Lyapunov exponents. The conditions for implementing and specific features of chaotic dynamic modes are revealed for films of three basic crystallographic orientations: (100), (110), and (111). It is shown that chaotic precession modes can be controlled using external magnetic fields. Time analogs of the Poincaré section of chaotic mode trajectories are considered.     

Resonance excitation of polaritons by bulk electromagnetic waves in the layered systems with anisotropic substrates

The possible resonance excitation of surface electromagnetic waves by the bulk waves at the interface between a positive transparent uniaxial crystal and an isotropic medium has been predicted. The existence of the surface waves is provided by anisotropy of one of the boundary media. The tensor relation between the vector amplitudes of an exciting bulk electromagnetic wave and the excited surface wave is established. The ratio of the moduli of the tangential components of these amplitudes is analyzed as a function of the angle of incidence and the polarization of the bulk wave. The numerical calculations are performed for the surface waves at the interface between paratellurite TeO₂ and a KRS-6 (TlBr 30%-TlCl 70%) crystal.     

Ideal gas in a box — a numerical study

A numerical study of the ideal monoatomic gas in a rectangular box is presented. The spatial distribution of temperature, density, pressure and chemical potential is studied in detail with and without the presence of gravitational forces. Some conclusions are drawn regarding the importance of the particle-wall interaction.     

X-ray diffraction by polydomain crystals modulated by transverse waves of atomic displacements. 1. Single-wave modulation in crystals

The intensity distributions of diffuse X-ray scattering caused by domains characterized by the transverse wave of atomic displacements polarized in the (010) plane and propagating along the [001] direction are calculated by numerical methods analyzed in the kinematical approximation. The regular changes in the intensity and half-width of the satellite peaks are revealed as functions of the wave amplitude and the average domain size. The characteristic features of diffraction are considered in the case where the defect-density wave in the crystal affects the parameters of the displacement wave.     

CVD金刚石薄膜亚表面层氢杂质对表面活化反应的影响

采用密度泛函理论平面波赝势法研究了氢杂质位于氢终止金刚石薄膜亚表面层中三种不同位点处时金刚石的结构变化,以及氢原子在三种金刚石薄膜表面上的吸附难易程度,并对表面活化反应进行了过渡态搜索以探究化学气相沉积(CVD)过程中金刚石薄膜亚表面层氢杂质对表面活化的影响.对比计算结果发现:生长过程中,亚表面层的氢杂质使其附近的金刚...     

Comparative analysis of methods for studying internal stresses in crystals

The possibilities provided by the main polarization optical methods of studying internal stresses in differently oriented plates prepared from cubic crystals are compared. A promising method for obtaining exhaustive information on the stressed state of an object, including the trajectories and the values of the principal stresses, is described.     

A Model for Soliton Excitations in (CH)x

We present a simple model for those properties of (CH)_x which are associated with the concept of solitions. We propose an “an initio” calculation of the wave function and energy of the soliton within an “Unrestricted Hartree-Fock” scheme. Electron-electron interactions are capable to originate an organization into domains and walls when described in terms of the so-called alterant orbitals of LÖWDIN. The essential features of the treatemnt are reviewed and numerical results are re ported. Then a connection is made between the model and some other formalisms. Finally we discuss a tent ative interpretation of electron spin resonance experiments. Specially emphasized are numerical simulations of spectra and analy sis of diffusive motions of solitons.     

On the nature of the heterogeneous dynamics of ions in ionic conducting glasses

Molecular dynamics simulations were performed to study the complex and heterogeneous dynamics of ions in ionically conducting glasses. The dynamics of Li ions in lithium silicate glasses have been characterized by van-Hove functions, fractal dimension of random walks, multifractal analysis of density profile, and principal component analyses of time series. Hierarchy dynamics with local and successive jumps, which are followed by cooperative jumps involving more ions, are observed in the self-part of the van-Hove functions and in trajectories where they form a multifractal density profile. Fractal dimensions of the random walks can be used to characterize the motions of ions in both the short and long length-scale regions. Difference between them becomes clearer in the glassy state, and the corresponding power law dependences of the mean squared displacements can be well explained by these exponents. Phase-space plot using the de-noised data obtained by principal component analysis reveals that the trajectory extending from the short time to the long time dynamics in the plot is continuous and has long term memory. The motion examined by the principal component analysis of the time series shows the deterministic character of the single particle ion dynamics. Each ion moves among domains of collective motion. Recurrence plot and mutual information function shows long correlation of the dynamics. Therefore, the cause of the dynamic heterogeneity is rather deterministic in nature.