The Character of Dislocations in LiCoO2

Dislocations in LiCoO2 were observed by transmission electron microscopy, and their Burgers vectors were determined by analysis of diffraction contrast in tilting experiments. The configuration of all dislocations indicates that they are glissile, and dislocation configurations were found that are indicative of active slip planes. Perfect dislocations of a/3 type Burgers vectors were observed on {0001} habit planes. These perfect dislocations sometimes dissociate into Shockley partial dislocations with a/3 type Burgers vectors. Glide of these partial dislocations can account for the sequence of crystal structures O3, H1-3, O1 that occur with the delithiation of LiCoO2. The presence of glissile dislocations also suggests possible damage mechanisms during cycling

Topological Gauge Theory Of General Weitzenbock Manifolds Of Dislocations In Crystals

General Weitzenbock material manifolds of dislocations in crystals Are proposed, the reference, idealized and deformation states of the bodies in general case are generally described by the general manifolds, the topological gauge field theory of dislocations is given in general case,true distributions and evolution of dislocations in crystals are given by the formulas describing dislocations in terms of the general manifolds,furthermore, their properties are discussed.Comment: 10pages, Revte

Impact of Screw and Edge Dislocation on the Thermal Conductivity of Nanowires and Bulk GaN

We report on thermal transport properties of wurtzite GaN in the presence of dislocations, by using molecular dynamics simulations. A variety of isolated dislocations in a nanowire configuration were analyzed and found to reduce considerably the thermal conductivity while impacting its temperature dependence in a different manner. We demonstrate that isolated screw dislocations reduce the thermal conductivity by a factor of two, while the influence of edge dislocations is less pronounced. The relative reduction of thermal conductivity is correlated with the strain energy of each of the five studied types of dislocations and the nature of the bonds around the dislocation core. The temperature dependence of the thermal conductivity follows a physical law described by a T$^{-1}$ variation in combination with an exponent factor which depends on the material's nature, the type and the structural characteristics of the dislocation's core. Furthermore, the impact of the dislocations density on the thermal conductivity of bulk GaN is examined. The variation and even the absolute values of the total thermal conductivity as a function of the dislocation density is similar for both types of dislocations. The thermal conductivity tensors along the parallel and perpendicular directions to the dislocation lines are analyzed. The discrepancy of the anisotropy of the thermal conductivity grows in increasing the density of dislocations and it is more pronounced for the systems with edge dislocations

On the non-uniform motion of dislocations: The retarded elastic fields, the retarded dislocation tensor potentials and the Li\'enard-Wiechert tensor potentials

The purpose of this paper is the fundamental theory of the non-uniform motion of dislocations in two and three space-dimensions. We investigate the non-uniform motion of an arbitrary distribution of dislocations, a dislocation loop and straight dislocations in infinite media using the theory of incompatible elastodynamics. The equations of motion are derived for non-uniformly moving dislocations. The retarded elastic fields produced by a distribution of dislocations and the retarded dislocation tensor potentials are determined. New fundamental key-formulae for the dynamics of dislocations are derived (Jefimenko type and Heaviside-Feynman type equations of dislocations). In addition, exact closed-form solutions of the elastic fields produced by a dislocation loop are calculated as retarded line integral expressions for subsonic motion. The fields of the elastic velocity and elastic distortion surrounding the arbitrarily moving dislocation loop are given explicitly in terms of the so-called three-dimensional elastodynamic Li\'enard-Wiechert tensor potentials. The two-dimensional elastodynamic Li\'enard-Wiechert tensor potentials and the near-field approximation of the elastic fields for straight dislocations are calculated. The singularities of the near-fields of accelerating screw and edge dislocations are determined.Comment: 31 pages, to appear in: Philosophical Magazin

Dislocations in uniaxial lamellar phases of liquid crystals, polymers and amphiphilic systems

Dislocations in soft condensed matter systems such as lamellar systems of polymers, liquid crystals and ternary mixtures of oil, water and surfactant (amphiphilic systems) are described in the framework of continuum elastic theory. These systems are the subject of studies of physics, chemistry and biology. They also find applications in the industry. Here we will discuss in detail the influence of dislocations on the bulk and surface properties of these lamellar phases. Especially the latter properties have only been recently studied in detail. We will present the experimental evidence of the existence of screw and edge dislocations in the systems and study their static properties such as: energy, line tension and core structure. Next we will show how does the surface influence the equilibrium position of dislocations in the system. We will give the theoretical predictions and present the experimental results on thin copolymer films, free standing films of liquid crystals and smectic droplets shapes. The surface is deformed by dislocations. These deformations are known as edge profiles. Surface deformations induce elastic interactions between edge dislocations. A new phenonenon discussed in our paper is the fluctuations induced interactions between edge dislocations.At suitable conditions edge dislocations can undergo an unbinding transition. Also a single dislocation loop in a smectic freely suspended film can undergo an unbinding transition. We shall also compute the equilibrium size of the loop contained between two hard walls. Finally we will discuss the dynamical bulk properties of dislocations such as: mobility (climb and glide),permeation, and helical instability of screw dislocations. Lubrication theory will also be discussed.Comment: plain TeX, 65 pages, review for International Journal of Modern Physics

Modelling of dislocation generation and interaction during high-speed deformation of metals

Recent experiments by Kiritani et al. have revealed a surprisingly high rate of vacancy production during high-speed deformation of thin foils of fcc metals. Virtually no dislocations are seen after the deformation. This is interpreted as evidence for a dislocation-free deformation mechanism at very high strain rates. We have used molecular-dynamics simulations to investigate high-speed deformation of copper crystals. Even though no pre-existing dislocation sources are present in the initial system, dislocations are quickly nucleated and a very high dislocation density is reached during the deformation. Due to the high density of dislocations, many inelastic interactions occur between dislocations, resulting in the generation of vacancies. After the deformation, a very high density of vacancies is observed, in agreement with the experimental observations. The processes responsible for the generation of vacancies are investigated. The main process is found to be incomplete annihilation of segments of edge dislocations on adjacent slip planes. The dislocations are also seen to be participating in complicated dislocation reactions, where sessile dislocation segments are constantly formed and destroyed.Comment: 8 pages, LaTeX2e + PS figures. Presented at the Third Workshop on High-speed Plastic Deformation, Hiroshima, August 200

Topological dragging of solitons

We put forward properties of solitons supported by optical lattices featuring topological dislocations, and show that solitons experience attractive and repulsive forces around the dislocations. Suitable arrangements of dislocations are even found to form soliton traps, and the properties of such solitons are shown to crucially depend on the trap topology. The uncovered phenomenon opens a new concept for soliton control and manipulation, e.g., in disk-shaped Bose-Einstein condensates.Comment: 15 pages, 5 figures, to appear in Physical Review Letter