Atoms In Crystal Lattice Research Articles

Experimental Analysis of Chemical Damage of Water to Soil Structure

Chemical components of the soil take an important role in the structure stability. It controls the soil structure under the normal water environment such as ordinary temperature, atmospheric pressure, and slowly changing hydro-chemical environment etc. It also has an important influence on the ground subsidence and the formation of soil caves as well as the collapse of dispersive soil. Scanning Electron Microscopy(SEM), CT technology and X diffraction were used to measure the chemical damage of water to the soil structure in the laboratory. Results indicate that under normal water environment, the change of the environmental parameters is not sufficient to cause damage to the internal crystal force of mineral intergranulars and to activate atoms in crystal lattice, which leads some defects and displacement of the crystal lattice. However, it can activate linking substance of clay grains be defined as “soil mini-structure”. As the greatest contributor of soil stability, the mini-structure is the "platform" and main place in which soil stability and instability will develop.

Comparative Analysis of Process of Diffusion of Interstitial Oxygen Atoms and Interstitial Hydrogen Molecules in Silicon and Germanium Crystals: Quantumchemical Simulation

AbstractA theoretical modeling and comparative analysis of the process of diffusion of the interstitial oxygen atoms and interstitial hydrogen molecules (H2) in silicon and germanium crystals at normal and hydrostatic pressure (HP) have been performed. The process of diffusion of particle with a strong interaction with a crystal lattice (interstitial oxygen atom) is a cooperative process. Three nearest Si (Ge) atoms of crystal lattice are involved in an elementary oxygen jump from a bond-center site to another bond-center site along a path in the (110) plane. It is precisely their optimum position (corresponding to a local minimum of the crystal total energy) determines the value of the diffusion parameters of an interstitial oxygen atom in silicon and germanium crystals. In a sense, the diffusion process may be considered as a diffusion process of qwasiparticle – (Oi+3Si). In the case of a particle weakly interacting with a crystal lattice (interstitial hydrogen molecules) we come up against the opposite case – the diffusion of H2 is not a cooperative process. The calculated values of the activation energy and pre-exponential factor for an interstitial oxygen atom δE(Si) = 2.59 eV, δE(Ge) = 2.05 eV, D0 (Si)= 0.28 cm2 s−1, D0 (Ge)= 0.39 cm2 s−1 and interstitial hydrogen molecule δE(Si) = 0.79 – 0.83 eV, δE(Ge) = 0.58 – 0.62 eV D0 (Si)= 7.4 10−4 cm2 s−1, D0 (Ge)= 6.510−4 cm2 s−1 are in an excellent agreement with experimental ones and for the first time describe perfectly an experimental temperature dependence of an interstitial oxygen atom and hydrogen molecules diffusion constant in Si crystals.

Local vibrational modes in crystal lattices with a simply connected region of the quasi-continuous phonon spectrum

It is shown that the use of the mode classification adopted in the Jacobi matrix method and which is the most natural one for describing localized states leads to extremely rapid convergence of the Green functions for frequencies lying outside the quasi-continuum band of the crystal. This has made it possible to obtain rather general analytical expressions for the conditions of formation and the characteristics of local modes due to the presence of light impurity atoms in crystal lattices having a simply connected region of the quasi-continuous phonon spectrum. The accuracy with which the frequencies and intensities of the local modes are determined using these expressions is illustrated for examples of light substitutional impurities (isotopic and weakly coupled) and close-packed structures (fcc and hcp) and also isolated pairs of isotopic impurities in an fcc crystal lattice. In particular, the results permit simple and extremely accurate evaluation of the parameters of the host lattice and defect from the known values of the local frequencies.

The influence of energy levels broadening on intersubband acoustic phonon scattering rates in quantum wire

The approach to take into account the influence of the energy levels broadening on the intersubband acoustic phonon scattering rates is developed. The roughness of the quantum wire boundaries and the oscillations of crystal lattice atoms are treated as the mechanisms causing the energy levels broadening. It is shown that the function of intersubband acoustic phonon scattering rate versus electron kinetic energy has no singularity points.

Mean-square displacements of metal and boron atoms in crystal lattices of rare-earth hexaborides

The intensities of the I410 and I411 reflections of nine rare-earth hexaborides MB6 (M=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy) are experimentally studied in the temperature range 4.2–300 K. The mean-square displacements of metal and boron atoms are calculated from the temperature dependences of the intensities I410(T) and I411(T). The characteristic temperatures of the metal (θM) and boron (θB) sublattices of rare-earth hexaborides are determined in the Debye approximation. It is found that the characteristic temperatures decrease with an increase in the atomic number of the metal.

Mechanics of a discrete chain with bi-stable elements

It has become common to model materials supporting several crystallographic phases as elastic continua with non (quasi) convex energy. This peculiar property of the energy originates from the multi-stability of the system at the microlevel associated with the possibility of several energetically equivalent arrangements of atoms in crystal lattices. In this paper we study the simplest prototypical discrete system—a one-dimensional chain with a finite number of bi-stable elastic elements. Our main assumption is that the energy of a single spring has two convex wells separated by a spinodal region where the energy is concave. We neglect the interaction beyond nearest neighbors and explore in some detail a complicated energy landscape for this mechanical system. In particular we show that under generic loading the chain possesses a large number of metastable configurations which may contain up to one (snap) spring in the unstable (spinodal) state. As the loading parameters vary, the system undergoes a number of bifurcations and we show that the type of a bifurcation may depend crucially on the details of the concave (spinodal) part of the energy function. In special cases we obtain explicit formulas for the local and global minima and provide a quantitative description of the possible quasi-static evolution paths and of the associated hysteresis.

Solid-state NMR and x-ray diffraction studies of ionic complex of 1,8-bis(dimethylamino)naphthalene (DMAN) with picrolonic acid

An ionic complex of 1,8-bis(dimethylamino)naphthalene with picrolonic acid was studied by 13C and 1H magic angle spinning and x-ray diffraction. Structural and spectroscopic features of this compound were investigated. The detailed x-ray structure of this complex is described. A multicentre model of hydrogen bonding in proton sponges {[Me2N—H· · ·NMe2]+· · ·Xδ−} is proposed and the influence of weak intermolecular intractions with the nearest electronegative atom in crystal lattice of a proton sponge on the strong intramolecular [N—H· · ·N]+ hydrogen bonding is demonstrated. It appears that weak interactions of electronegative atoms with the nearest methyl hydrogen atoms can influence the localization of the proton in the intramolecular [N—H· · ·N]+ hydrogen bridge. © 1997 John Wiley & Sons, Ltd.

Focused high-voltage electron beams in material science

High-voltage electron microscopes (HVEMs) have become well established instruments in material science during the past three decades. Apart from the high penetration strength which permits investigations of comparatively thick specimen foils, HVEMs provide the means for a variety of in situ specimen manipulations such as heating, cooling, deformation and large angle tilting, which are the basis for a wide range of applications. Four examples will be discussed: (1) imaging with atomic resolution with the Stuttgart JEOL ARM1250 microscope; (2) the detailed study of the displacement process of crystal atoms from their regular lattice sites; (3) electron channelling, which can supply information about the location of specific atoms in crystal lattices; (4) the emission of coherent bremsstrahlung from small crystal areas.

Mossbauer relaxation spectra of crystal lattice atoms in the presence of diffusing interstitial defects

The Mossbauer relaxation spectra of crystal lattice atoms in the presence of diffusing interstitial defects is studied. The relaxation effects are a consequence of the fluctuating interstitial configurations around each Mossbauer atom, causing hyperfine interaction-induced modulations of the gamma energy. The relaxation spectra in the limits of fast and slow relaxation are calculated exactly, and an approximate expression in the intermediate relaxation range is given. The results allow the determination of interstitial diffusion rates from measured Mossbauer relaxation spectra.

Application of particle channeling to the study of a cooperative Jahn-teller phase transition in nickel chromite

Development of particle channeling in single crystals has led to a number of important applications in studies of impurity ions in solids, crystal surface structures and decay of short-lived compound nuclei. In all of these cases the crucial property is the ability of channeled particles to distinguish spatial positions of crystal lattice atoms or impurity atoms with high accuracy. This property of channeled ions suggests potential application to studies of crystalline phase transitions, thermal motion of lattice atoms and investigation of the dynamic and static behavior of “off center” or Jahn-teller impurity ions. We report here on an experimental demonstration of these possibilities in a channeling study of a reversible cooperative Jahn-teller transition in nickel chromite. In these experiments the angular dependence of the normalized backscattering yields of 1.5 MeV helium ions from a NiCr 2O 4 single crystal close to the [111], [110], [11 1] , [211] and [12 1] crystallographic axes has been measured for va temperatures above and below and below the transition temperature. At the transition temperature an abrupt change in direction of the crystal axes was observed. In addition, the minimum yield of the channeling dips was found to change significantly.

Electron Wave Optical Identification of Specific Atoms in Thin Crystals

The Abbe's prediction about the ultimate resolution of lens acquired a deeper significance for the realization of new type of microscope when the diffraction of electrons was confirmed in accord with de Broglie's theory. However, it was only early 1970's that heavy atoms and well-defined molecules were brought to human eyes in spite of the tremendous progress in modern science. On the occasion of commemorating the 50th anniversary of electron diffraction, it may be worthwhile to note that the resolution of "microscope", which was once resigned to discouraging limitation, has been improved so surprisingly that even oxygen atoms in crystal lattice can be identified in some fortuitous case.

On the mechanism of chemical diffusion in solids and its application to oxidation

The participation of crystal lattice atoms in an elementary act of chemical diffusion may have a collective nature. This involves a consecutive elastic translation of activated complexes, the distorted regions possessing more mobility than an equivalent quantity of point defects. Thermodynamic analysis shows that participation of an activated complex occurs during chemical diffusion. This model is applied to the kinetics of the oxidation of metals. The apparent activation energy of the process is considerably lower in this case than in the case of self-diffusion in the lattice. It is shown that there exists a limiting thickness of the scale above which further growth occurs at the cost of point defect motion with a lower rate.

THE EFFECT OF CHANNELING ON DISPLACEMENT CASCADE THEORY

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