Anisotropy of structural models for amorphous materials

Abstract

Correlations responsible for anisotropic-scattering properties of close-packed and tetrahedrally coordinated amorphous-model structures are discussed. It is shown that although there are regular planes of high density associated with the strong-scattering directions, the scattering anisotropy is not very different from that which occurs for random scattering.

Medium-range structure in glasses and low-Q structure in neutron and X-ray scattering data

“…Gaskell and Wallis [13] calculated the anisotropic scattering, S(Q) for jQj = Q 1 , from models for a-SiO 2 using the method described by Alben et al [16]. They concluded that the highest values of the anisotropic intensity, in those models that were most successful in describing the FSDP in silica, were associated with planar fluctuations in atomic density.…”

NCM — Looking back — Moving forward

“…Here, the concepts of randomness become useful. The relation quoted by Alben et al [11], shows that there is a probability of 0.1 that chance correlations from a random model of this size would lead to I(Q) values greater than about 8 times the average intensity. Fig.…”

“…Fig. 2b shows an even more extreme distribution of the scattered intensity [12] for a section of Finney's 7994-atom, dense random packed model for an amorphous metal [13], where the maximum intensity is almost 14 times the average [11]. This is what examination of anisotropy in CRN models can offer, emphasising the potential value of data extracted from anisotropic scattering in real materials.…”

“…The highest peak, corresponds to a relative intensity I(Q)/I(Q) = 10.5. This is significantly more than that calculated for a collection of random scatterers, for which the intensity would be less than 8.1 at a probability of 0.1 (using the relation given by Alben et al [11]). (b) A similar diagram, calculated [12] for the central 549 atoms of Finney's dense random packed model for liquid and glassy metals [13].…”

“…(b) A similar diagram, calculated [12] for the central 549 atoms of Finney's dense random packed model for liquid and glassy metals [13]. Here, the anisotropic scattered intensity is 13.8, corresponding to a probability of about 1% expected for random fluctuations [11].…”