No abstract available

[en] The formation and migration energies of vacancies in crystals under hydrostatic strain are considered in model fcc and bcc crystals using the technique of computer simulation. Equilibrium and non-equilibrium interatomic potentials have been employed for iron, molybdenum, copper and nickel. In the case of Ni, a simple density-dependence of the potential has also been incorporated. Significant differences between the potential forms and crystal structures are reported. For the purpose of comparison, Mukherjee's empirical relation between the formation energy and Debye temperature is exploited to obtain the variation of this energy with lattice parameter. By way of contrast, the effect of the vacancy migration energy of a neighbouring vacancy is also considered in the model crystals. (orig.)

[en] We examine quantitatively the effects on tracer diffusion of both externally applied strains and internal strains generated by large interstitial particles dissolved in a coherent hard-sphere crystal. The molecular-dynamics method, generalized to permit elastic deformations of a system, is used to simulate the diffusion of interstitials in a binary hard-sphere solid. A tracer-diffusion response function E(k) is calculated from a tracer density-density correlation function. The associated diffusivity D is found to be independent of crystallographic orientation at long wavelengths. The simulation results are further interpreted by using a multiclass master equation to describe particle transitions and by using elasticity theory. The diffusivity obtained can be characterized very accurately by an activation entropy that is proportional to the square of the radius of an interstitial. Finally, the application of an external strain can modify the symmetry of the lattice, and the diffusion tensor associated with the deformed lattice must be modified in a manner consistent with elastodiffusion theory

[en] Interstitial loops are one of the principal evolving defects in irradiated materials. The evolution of interstitial loops, including spatial and size distributions, affects both vacancy and interstitial accumulations in the matrix, hence, void formation and volumetric swelling. In this work, a phase-field model describing the growth kinetics of interstitial loops in irradiated materials during aging is developed. The diffusion of vacancies and interstitials and the elastic interaction between interstitial loops and point defects are accounted in the model. The effects of interstitial concentration, chemical potential, and elastic interaction on the growth kinetics and stability of interstitial loops are investigated in two and three dimensions. It is found that the elastic interaction enhances the growth kinetics of interstitial loops. The elastic interaction also affects the stability of a small interstitial loop adjacent to a larger loop. The model predicts linear growth rates for interstitial loops that is in agreement with the previous theoretical predictions and experimental observations

[en] In recent years, significant progress has been made in understanding the void growth and swelling behaviour in metals under cascade damage conditions in terms of differences in the intra-cascade clustering of self-interstitials (SIAs) and vacancies, and the thermal stability and (one-dimensional) mobility of the resulting clusters. The problem of void nucleation was, however, not treated in any detail within this 'production bias model'. In treating void nucleation, the following experimental findings have to be considered: (1) Both nucleation and growth of voids are much more efficient under cascade damage conditions than under electron irradiation. (2) Void nucleation occurs at low dose, particularly in pure metals, and tends to saturate at higher doses. (3) There are significant differences in the void nucleation behaviour between pure metals of different crystal structure and between pure metals and alloys. In the present contribution, we discuss these findings in terms of a production bias controlled vacancy supersaturation rising in the transient to quasi-steady-state and falling during cascade damage accumulation, and thus inducing a limited void nucleation pulse, the yield of which represents the experimentally observed saturated void density

No abstract available

[en] A method is developed for analyzing defect-diffusion coefficients. Defect diffusion is an integral part of considerations in diffusion theory for atom motion in crystals, but it has not been developed as a distinct concern in diffusion kinetics. An ''alloy'' of tracer and nontracer atoms occupying octahedral interstices of the fcc lattice has been used as a model to develop quantitative descriptions of site blocking, correlation, and flow effects that are all characteristic elements of defect-diffusion kinetics. Correlated walk of vacancies in and near a divacancy can be discussed using these results, and this analysis suggests a method for generalizing theoretical treatments of atom-defect and defect-defect interactions in diffusion-related phenomena

[en] Short note. 1 ref

[en] Photonic crystals are extremely sensitive to structural disorder even to the point of completely losing their functionalities. While, on one side, this can be detrimental for applications in traditional optical devices, on the other side, it gives also rise to very interesting new physics and maybe even new applications. We propose a route to introduce disorder in photonic crystals in a controlled way by creating a certain percentage of vacancies in the lattice. We show how the method works and what type of materials can be obtained this way. Also, we use this system to probe the role of disorder on the resulting transport properties from various points of view, including measurements of the transport and scattering mean free path and the diffusion constant.

[en] To describe the stress influence on diffusion flows in interstitial alloys, we use an approach, developed earlier for the case of vacancy mechanism. This approach, opposite to most other known ones, takes into account the atomic structure in the neighborhood of the defect and the stresses, that could modify the energy of a jumping atom through the displacement field not only at the atom site but also in a saddle position. Apart from this, it takes the shear stresses into consideration that can modify the frequency of jumps through the displacement field at the site and saddle position. Stress fields alter the surrounding atom configuration and, as a consequence, the height of the activation barrier is changed. Knowing these changes it is possible to calculate the jump rate and to obtain expressions for the interstitial diffusion fluxes in FCC and BCC structures. In these nonlinear equations, influence of the deformation tensor component on diffusion flux is determined by coefficients depending on atom interaction. The diffusion processes under pressure are analyzed by using the obtained equations. Expressions for the activation volume of the interstitial solute diffusion are obtained. Interstitial redistribution near the defects, such as dislocation or crack orifice is also analyzed