Structural defects in amorphous solids Statistical analysis of a computer model

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-type defects on the radial distribution function was further studied, and it was shown that the effect is similar to that experimentally observed when annealing an amorphous alloy at temperatures below the glass transition temperature.