Neutron scattering from vitreous silica: III. Elastic diffraction

Abstract

The differences between elastic and total neutron diffraction experiments on amorphous solids are discussed quantitatively using data for vitreous SiO 2. It is shown that in the former case early peaks in the real space correlation function T(r) are broader due to the inclusion of the effects of acoustic phonons and that for vitreous silica the atomic thermal vibrations, relative to the SiO bond direction, are approximately isotrpic. The two techniques yield the same SiO bond length, indicating that recoil corrections are unnecessary in total diffraction studies of amorphous solids. Supplementary constant Q scans across ω- Q space at high Q are qualitatively in agreement with a simple twin Gaussian model for the scattering law S( Q, ω), which may prove useful in studying the effects of static approximation distortions.