While in amorphous forms its composition can continuously vary between SiO2 (silica) and Si3N4 (silicon nitride), the only known intermediate crystalline phase is Si2N2O.

[2] It is found in nature as the rare mineral sinoite in some meteorites and can be synthesized in the laboratory.

The strong covalent bonding of this structure results in high flexural strength and resistance to heating and oxidation up to temperatures of about 1600 °C.

SiON materials thus obtained are referred to as polymer derived ceramics or PDCs.

Quaternary silicon oxynitrides containing a lanthanide element, such as La, Eu or/and Ce are used as phosphors.