https://www.tcd.ie/Physics/people/Graham.Cross/SF%20Poster%202011/Schuh-ActaMater07-Mechanical%20behaviour%20of%20amorphous%20alloys.pdf

Mechanical behavior of amorphous alloys

A simple form of multi-ion interaction has been constructed for the purpose of atomistic simulation of transition metals. The model energy consists of a bonding term, which is the square-root of a site density ρi, summed over atoms i, and a repulsive pairwise term of the form The site density ρi is defined as sum over neighbouring sites j of a cohesive potential (R ij). Both V and are assumed to be short-ranged and are parameterized to fit the lattice constant, cohesive energy and elastic moduli of the seven body-centred-cubic (b.c.c.) transition metals. The result is a simple model which, unlike a pair-potential model, can account for experimental vacancy-formation energies and does not require an externally applied pressure to balance the “Cauchy pressure”.

A simple empirical N-body potential for transition metals

Thermal conductivity of carbon nanotubes and their polymer nanocomposites: A review

http://nathan.instras.com/documentDB/paper-44.pdf

Surface photovoltage phenomena: theory, experiment, and applications

Atomic-level structure and structure–property relationship in metallic glasses

A definition of structural defects in amorphous solids in terms of the distribution of the internal stresses on the atomic level and of the symmetry of the environment of individual atoms is introduced. This definition does not require an ideal reference structure. The concept of the internal stresses on the atomic scale has been previously applied to describe the core structure of crystalline dislocations. In this paper it has been applied to the model amorphous structure generated by a computer simulation. It was found that there is a significant variation in the magnitude and direction of internal stresses, and that there are regions of 10 to 20 atoms over which the stresses remain either high or low. A method of calculating the symmetry coefficients at atomic sites has been proposed, and applied to the same system. It has been shown that there are significant correlations between the internal stresses and the local symmetry. The low-stress, high-symmetry regions resemble microcrystalline clus...

Structural defects in amorphous solids A computer simulation study

The possibility of defining structural defects in amorphous solids in terms of parameters such as atomic-level internal stresses and local symmetry coefficients was proposed in a previous paper (Egami, Maeda and Vitek 1980). Using a model amorphous structure generated by a computer, these parameters are statistically analysed in the present paper. It is shown that the stress and the symmetry coefficients are closely correlated and that spatial correlations of various kinds exist. The structural defects are then defined as regions in which the corresponding characterizing parameter deviates significantly from its average value. Two distinct classes of defects were found; (i) positive (p-type defects) and negative (n-type defects) local density fluctuations; and (ii) regions of large shear stresses and large deviations from spherical symmetry. Defects consisting of pairs of p-type and n-type defects separated by regions of large shear stresses are also common. The effect of annihilation of p- and n...

Structural defects in amorphous solids Statistical analysis of a computer model

A one‐to‐one correspondence between deformation‐produced dark spots in cathodoluminescence (CL) micrographs and dislocations has been demonstrated in n‐type CdTe by comparing the CL pattern with the etch‐pit pattern developed with a new etchant which has been ascertained to reveal dislocations by a successive polishing and etching method.

Observation of dislocations in cadmium telluride by cathodoluminescence microscopy

Transmission electron microscopic studies have been performed on lattice defects in 6H silicon carbide single crystals; the crystals were subjected to microhardness indentation tests between room temperature and 1200°C and then to uniaxial compression at temperatures from 1100 to 1650°C. It was observed that their basal dislocations, the main defects introduced by deformation, were dissociated into Shockley partials separated by very wide stacking faults, the energy of which was evaluated to be 2.5 ± 0·9 mJ m−2. The lineshapes of the partials varied considerably, depending on the sign and angle (with the dislocation line) of the Burgers vector; this suggests that the mobility of the partials is affected by the geometry of dislocations. The fact that basal dislocations were aligned more or less in crystallographic 〈1120〉 directions indicates the presence of a high Peierls potential. Macroplastic deformation was observed above 1000°C. This critical temperature seems to be determined by the motion o...

Defects in plastically deformed 6H SiC single crystals studied by transmission electron microscopy

Effects of 30‐keV electron‐beam irradiation on dislocation glide were investigated for α‐ and β‐dislocations in bulk n‐GaAs single crystals by cathodoluminescence microscopy using a scanning electron microscope with a bending apparatus in it. At high temperatures above Tc, the electron irradiation has no effect on dislocation velocity v and the temperature dependence v(T) follows an Arrhenius formula v0d exp(−Ed/kT). Below Tc, v(T) under irradiation breaks off the above relation and is enhanced following another Arrhenius formula v0i exp(−Ei/kT). The enhancement effect is completely reversible for individual dislocations. From measurements of irradiation intensity I and stress τ dependences, the dislocation velocity was found to be expressed by a unified formula v=v0d exp[−Ed(τ)/kT ]+v*i(I/I0)0.84  exp{−[Ed(τ)−ΔE]/kT}, which is explained by neither a heating effect nor a charge state effect, but the recombination enhanced defect motion (REDM) mechanism. In view of the REDM mechanism, the ΔE (∼0.7 eV for α...

Koji Maeda

Papers

Structural defects in amorphous solids A computer simulation study

Structural defects in amorphous solids Statistical analysis of a computer model

Observation of dislocations in cadmium telluride by cathodoluminescence microscopy

Defects in plastically deformed 6H SiC single crystals studied by transmission electron microscopy

Quantitative measurements of recombination enhanced dislocation glide in gallium arsenide