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arXiv · 0909.2457

The static structure factor of amorphous silicon and vitreous silica

Adam M. R. de Graff·M. F. Thorpe
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Abstract

Liquids are in thermal equilibrium and have a non-zero static structure factor S(Q->0) = [ - ^2]/ = rho*k_B*T*Chi_T where rho is the number density, T is the temperature, Q is the scattering vector and Chi_T is the isothermal compressibility. The first part of this result involving the number N (or density) fluctuations is a purely geometrical result and does not involve any assumptions about thermal equilibrium or ergodicity and so is obeyed by all materials. From a large computer model of amorphous silicon, local number fluctuations extrapolate to give S(0) = 0.035+/-0.001. The same computation on a large model of vitreous silica using only the silicon atoms and rescaling the distances gives S(0) = 0.039+/-0.001, which suggests that this numerical result is robust and similar for all amorphous tetrahedral networks. For vitreous silica, we find that S(0) = 0.116+/-0.003, close to the experimental value of S(0) = 0.0900+/-0.0048 obtained recently by small angle neutron scattering. More detailed experimental and modelling studies are needed to determine the relationship between the fictive temperature and structure.

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Adam M. R. de Graff, M. F. Thorpe. 2009-09-14. The static structure factor of amorphous silicon and vitreous silica. https://arxiv.org/abs/0909.2457

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