The structure of SiO2 — Current views

Abstract Silicon dioxide or silica, one of the most important raw materials in ceramics, undergoes rather complex phase transformations under varying conditions of temperature, pressure and chemical purity. The flexibility of the silica framework, consisting of [SiO4] tetrahedra bonded together into a giant polymeric “open molecule” by sharing oxygen atoms, is primarily due to the easy adjustment of the SiOSi angles between tetrahedra in response to changing conditions. The structure reinvestigations of silica polymorphs done in recent years allow a comprehensive review of the structure problems, including the high-pressure and amorphous states of SiO2 and the mechanism of some of the phase transformations. The most difficult and still controversial problem of the structure of vitreous silica is rather extensively discussed in view of the technical importance of silica glass.