Silicon nitride oxide, dinitride disilicon oxide
|Molar mass||100.18 g·mol−1|
|Space group||Cmc21 No 36, Pearson symbol oS20|
|Lattice constant||a = 0.48553 nm, b = 0.52194 nm, c = 0.52194 nm, Z = 4|
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Silicon oxynitride is a ceramic material with the chemical formula SiOxNy. While in amorphous forms its composition can continuously vary between SiO2 (silica) and Si3N4 (silicon nitride), the only known intermediate crystalline phase is Si2N2O. It is found in nature as the rare mineral sinoite in some meteorites and can be synthesized in the laboratory.
The crystalline structure of silicon oxynitride is built by SiN3O tetrahedra connected through oxygen atoms along the c axis and through nitrogen atoms perpendicular to it. 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.
Polycrystalline silicon oxynitride ceramics are produced by nitridation of a mixture of Si and silicon dioxide at a temperature above melting point of silicon (1414 °C), in the range 1420–1500 °C:
- 3 Si + SiO2 + 2 N2 → 2 Si2N2O
Thin films of silicon oxynitride can be grown on silicon using a variety of plasma deposition techniques and used in microelectronics as a dielectric layer alternative to silicon dioxide and silicon nitride with the advantages of low leakage currents and high thermal stability. These films have an amorphous structure and therefore their chemical composition can widely deviate from Si2N2O. By changing the nitrogen/oxygen ratio in these films, their refractive index can be continuously tuned between the value of ~1.45 for silicon dioxide and ~2.0 for silicon nitride. This property is useful for gradient-index optics components such as graded-index fibers.
Silicon oxynitrides can be doped with metal atoms. The most common example is sialon, a family of quaternary SiAlON compound. Quaternary silicon oxynitrides containing a lanthanide element, such as La, Eu or/and Ce are used as phosphors.
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