Dislocation Core Energy Research Articles

Selective Etch for New Edge Dislocations in Sodium Fluoride

A simple etch consisting of a dilute aqueous solution containing manganous ions has been found to selectivity etch new edge dislocations in sodium fluoride. With this etch the new edge dislocations produced deep pits based on the icositetrahedral form, whereas all other dislocations yielded shallow cones. The selective etching action was decreased with increase of manganous ion concentration and with increase of the impurity content of the edge dislocation. The selective etching action is attributed to the combined effect of the elastic energy and the core energy of the new edge dislocation.

Polytypism and recombination radiation in pn junctions obtained by diffusing boron into n-type SiC

Large-scale first-principles calculations were performed to determine the stability and mobility properties of screw dislocations in common silicon carbide polytypes (4H, 2H and 3C). There is a profound lack of knowledge regarding these dislocations, although experimental observations show that they govern the plastic behavior of SiC at low temperature. Numerical simulations reported in this paper indicate that these dislocations are characterized by a shuffle core, the associated Peierls stress of which ranges from 8.9 to 9.6 GPa depending on the polytype. The only other stable dislocation core exhibits a reconstruction along the dislocation line, with a greater stability, but is also found to be sessile. Polytypism has a weak influence on these results, especially regarding dislocation core energies and Peierls stress. However, a qualitative difference is predicted between the cubic and the hexagonal systems regarding slip planes, with a possible dislocation displacement along a prismatic plane on average, which would result from a zigzag motion of the screw dislocations at the atomic scale.

Absorption spectrum in the vacuum ultraviolet and corresponding electron transitions in CdS

Large-scale first-principles calculations were performed to determine the stability and mobility properties of screw dislocations in common silicon carbide polytypes (4H, 2H and 3C). There is a profound lack of knowledge regarding these dislocations, although experimental observations show that they govern the plastic behavior of SiC at low temperature. Numerical simulations reported in this paper indicate that these dislocations are characterized by a shuffle core, the associated Peierls stress of which ranges from 8.9 to 9.6 GPa depending on the polytype. The only other stable dislocation core exhibits a reconstruction along the dislocation line, with a greater stability, but is also found to be sessile. Polytypism has a weak influence on these results, especially regarding dislocation core energies and Peierls stress. However, a qualitative difference is predicted between the cubic and the hexagonal systems regarding slip planes, with a possible dislocation displacement along a prismatic plane on average, which would result from a zigzag motion of the screw dislocations at the atomic scale.

Nucleation of surface pits by the condensation of vacancies

Abstract Small surface pits were observed to form on electropolished (111) surfaces of aluminium single crystals during cooling from elevated temperatures. The formation of these pits was attributed to the condensation of vacancies from the supersaturation produced during cooling at the points of intersection of dislocations with the surface. A finite temperature drop, δT, which was a function of the holding temperature, T h, was required to nucleate the pits. The principles of statistical mechanics when applied to vacancy clustering led to an equation which quantitatively predicted δT as a function of T h. The temperature dependence of the nucleation phenomenon was experimentally measured and found to be consistent with the theoretical predictions. The experimental results led to a corrected value of 1·8 × 10−5 ergs/cm (0·3 ev/plane) for the average dislocation core energy per unit length in aluminium.

Effect of Temperature on the Deformation of KCl-KBr Alloys

At low temperatures, ionic solids of the rock-salt structure deform by planar {110} slip and are brittle; at higher temperatures slip can occur on any plane of the <110> zone and fully ductile behavior is observed. The effect of alloying on this pattern of behavior has been studied for the KCl-KBr system. Pure polycrystalline KCl and a 0.6% KBr alloy are shown to be ductile at temperatures above 250°C, but a 1.3% alloy polycrystal remains brittle up to 350°C. Associated with this brittleness is the persistence of planar slip to much higher temperatures. More concentrated KBr additions suppress wavy glide in single crystals to temperatures approaching the melting point of the alloys. Data are presented to demonstrate the effect of KBr additions on the yield strength, work-hardening rate, and fracture stress of polycrystalline KCl and two dilute alloys. Small solute additions appear to influence work-hardening behavior much more than the yield strength, but more concentrated additions increase both significantly. The effect of KBr additions on glide behavior appears to be associated with changes in the core energies of dislocations of the <110> zone. Although the glide behavior of pure ionic crystals can be related to the polarizability of the constituent ions, a similar correlation is invalid for ionic solid solution alloys.