TEMPERATURE-DEPENDENCE OF THE 1ST SHARP DIFFRACTION PEAK IN VITREOUS SILICA

The temperature dependence of the first sharp diffraction peak (FSDP) in the neutron structure factor has been measured from room temperature to 1036-degrees-C. With increasing temperature, the FSDP decreases in amplitude in a normal fashion. This is in contrast to the anomalous temperature dependence of the FSDP that is typically observed in covalent oxide and chalcogenide glasses. The change in height of the FSDP with temperature is the result of a competition between an increase in the amplitude of thermal vibration at higher temperature and a diminished frustration at lower density. The normal behavior of the FSDP in vitreous silica is the consequence of an essentially zero thermal-expansion coefficient so that the effect due to thermal vibrations dominates. A structural rearrangements at elevated temperatures is also indicated.