Temperature dependence of the first sharp diffraction peak in vitreous silica

Abstract

Diffraction measurements on glasses often generate a structure factor with a prominent first sharp diffraction peak (FSDP). A temperature dependent change in the FSDP is most often attributed to two competing effects. Reduced frustration arising from a lower density tends to increase the intensity and decrease the width, while thermal vibrations tend to decrease the intensity and increase the width. In covalent glasses, the FSDP typically broadens and decreases in height with increasing temperature. Most oxide and chalcogenide glasses display a reversibly increasing FSDP with increasing temperature. Although vitreous silica (SiO{sub 2}) has been extensively researched, only Soklakov et al. have investigated its structure factor at elevated temperatures. They concluded that the temperature dependence of the FSDP (observed in x-ray diffraction patterns) was comparable to other oxide and chalcogenide glasses. Vitreous SiO{sub 2}, however, has an extremely small coefficient of thermal expansion (0.55 {times} 10{sup {minus}6}cm/cm C{degree}). Consequently its density varies little with temperature and an increase in the intensity of its FSDP is not expected. The purpose of this study is to determine the temperature dependence of the FSDP in vitreous silica using modern methods of neutron scattering. 9 refs., 1 fig., 2 tabs.