J. S. Koehler

Bio: J. S. Koehler is an academic researcher from University of Illinois at Urbana–Champaign. The author has contributed to research in topics: Vacancy defect & Dislocation. The author has an hindex of 23, co-authored 26 publications receiving 2994 citations. Previous affiliations of J. S. Koehler include Carnegie Institution for Science.

Space Charge in Ionic Crystals. I. General Approach with Application to NaCl

Abstract: The defect distribution in an ionic crystal is calculated for both pure crystals and crystals containing divalent cationic impurities. By taking the electrostatic energy into account explicitly, it is shown that bulk electrical neutrality and space-charge regions surrounding the vacancy sources are an inherent aspect of thermal equilibrium. Interactions among defects of the opposite charge are taken into account using the nearest-neighbor-binding model. Inclusion of the long-range effects of the Coulomb interaction and the question of the sign of charged dislocations are discussed.

Interaction of Dislocations with an Applied Stress in Anisotropic Crystals

Abstract: The equilibrium shape of a dislocation segment between two pinning points in the same glide plane is calculated. The assumption is made that the dependence of the dislocation self-energy on the geometry of the dislocation line can be expressed by using an energy per unit length, $E$, which is a function only of the angle, $\ensuremath{\theta}$, between the Burgers vector and the tangent to the dislocation. Only glide of the dislocation, not climb, is considered. The results obtained are compared with those for elastically isotropic crystals. It is found that the character of the dislocation shape is altered considerably if $E+\frac{{d}^{2}E}{d{\ensuremath{\theta}}^{2}}$ can be negative. It is suggested that the change in sign of this quantity is associated with diffusionless phase changes.

The Continuum Theory of Lattice Defects

Abstract: Publisher Summary The chapter presents a discussion on the continuum theory of lattice defects. The continuum analog of a crystal containing imperfections is an elastic body in a state of stress not produced by surface and body forces. The appropriate tool for handling the “continuum theory of lattice defects” is thus the usual theory of elasticity modified to include internal stress. Unlike the residual stresses encountered in engineering practice, these internal stresses have to be considered as capable of moving about in the medium. Recent interest in solid state physics has stimulated further development. The discussion of this chapter emphasizes on some of the background principles and illustrates them by specific examples chosen to bring out the peculiar features involved. Naturally, the continuum theory can hardly be expected to answer questions of current interest about the more intimate behavior of lattice defects (for example, the binding energy of two adjacent point defects). On the other hand, the theory perhaps suffers from the disadvantage that its limitations are more immediately obvious than are those of other approximate methods that have to be used in dealing with the solid state, for it sometimes gives good results even in what appear to be extreme cases. The theory of elasticity is concerned with the relation between the deformation of a body and the energy content of itself and its surroundings. The chapter also discusses specification of internal stress, including the Somigliana dislocations and the incompatibility tensor.

Nanoionics: ion transport and electrochemical storage in confined systems.

Abstract: The past two decades have shown that the exploration of properties on the nanoscale can lead to substantially new insights regarding fundamental issues, but also to novel technological perspectives. Simultaneously it became so fashionable to decorate activities with the prefix 'nano' that it has become devalued through overuse. Regardless of fashion and prejudice, this article shows that the crystallizing field of 'nanoionics' bears the conceptual and technological potential that justifies comparison with the well-acknowledged area of nanoelectronics. Demonstrating this potential implies both emphasizing the indispensability of electrochemical devices that rely on ion transport and complement the world of electronics, and working out the drastic impact of interfaces and size effects on mass transfer, transport and storage. The benefits for technology are expected to lie essentially in the field of room-temperature devices, and in particular in artificial self-sustaining structures to which both nanoelectronics and nanoionics might contribute synergistically.

Flux vortices and transport currents in type II superconductors

Abstract: This article is concerned with the mechanisms by which type II superconductors can carry currents. The equilibrium properties of the vortex lattice are described and the generalized driving force in gradients of temperature and field is derived using irreversible thermodynamics. This leads to expressions for thermal cross effects which can include pinning forces. The field distributions which occur in a range of situations are derived and a number of useful solutions of the critical state given. In particular, the distribution in a longitudinal field is obtained, and the conditions under which force-free configurations can break down by the cutting of vortices discussed. The effects of lattice rigidity on the summation of pinning forces is considered and it is shown that a summation based on statistical arguments uses the same approximations and leads to the same results as a dissipation argument. Theoretical expressions are derived for the vortex pinning interaction to a number of different metallurgical...

Colloquium : The glass transition and elastic models of glass-forming liquids

Abstract: Basic characteristics of the liquid-glass transition are reviewed, emphasizing its universality and briefly summarizing the most popular phenomenological models. Discussion is focused on a number of alternative models which one way or the other connect the fast and slow degrees of freedom of viscous liquids. It is shown that all these ``elastic'' models are equivalent in the simplest approximation.