# Oxonitridosilicate

The oxonitridosilicates, also called sions (Si + O + N) or silicon-oxynitrides are inorganic ceramic compounds in which oxygen and nitrogen atoms are bound to a silicon atom. A common variant also has aluminium replacing some silicon. They can be considered as silicates in which nitrogen partially replaces oxygen, or as nitridosilicates with oxygen partly replacing nitrogen.

## Formation

A possible way to make these compounds is to heat metal oxides or carbonates with silicon nitride and silica in a nitrogen atmosphere.

## Properties

Oxonitridosilicates have diverse structures. At the small scale silicon forms tetrahedral shapes surrounded by four oxygen or nitrogen atoms. With oxygen, one point of a tetrahedron can be bridged to another denoted O$^{[2]}$, or the oxygen can be a terminal atom denoted O$^{[1]}$. With nitrogen, it can be shared in more ways: terminal N$^{[1]}$, bridged between two tetrahedra N$^{[2]}$, or even three or four: N$^$, N$^{[4]}$. With nitrogen, tetrahedra can be fused on an edge, or a point, whereas oxygen only connects tetrahedra at a vertex.
The condensation ratio, denoted by K indicates how condensed the tetrahedra are. K is the number of silicon atoms divided by the sum of oxygen and nitrogen. For SiN$_4$$^{8−}$ or SIO$_2$$^{4+}$ K is 1/4 and it increases to 1/2 for SiO$_2$.

## Use

Oxonitridosilicates doped with europium have been used as phosphors in white LEDs, as they convert some blue light to other colours that can mix to white.

## Listing

| name | formula | crystal system | space group | unit cell | volume | phosphor colour Eu$^{2+}$ | comments |
| | LiSiNO | | | | | | |
| | Li$_3$SiNO$_2$ | | | | | | |
| | Li$_6$SiN$_2$O$_2$ | | | | | | |
| | Li$_7$SiN$_3$O | | Fm3m | a=4.6994 | | | |
| | Li$_5$SiNO$_3$ | | | | | | |
| | Na$_3$SiNO$_2$ | | | | | | |
| | CaSi$_2$O$_2$N$_2$ | | | | | | |
| | Ca$_{2.89}$Si$_2$N$_{1.76}$O$_{4.24}$ Ca$_3$Si$_2$O$_4$N$_2$ | cubic | Pa3 | a = 15.0626 Å V = 3417.45 Å$^3$ Z=24 | | green | colourless |
| | SrSi$_2$O$_2$N$_2$ | | | | | green | |
| | Li$_4$Sr$_4$[Si$_4$O$_4$N$_6$]O | tetragonal | P4$_2$/nmc | a=7.4833, c = 9.8365 V=552.81 Z = 2 | | orange | band gap 3.6 eV |
| | Sr$_3$Si$_{13}$Al$_3$O$_2$N$_{21}$ | orthorhombic | | a = 9.037, b = 14.734, c = 7.464 | | green | |
| | Y$_4$SiO$_7$N$_2$ | | | | | | |
| | BaSi$_2$O$_2$N$_2$ | | | | | bluish green | |
| | Ba$_3$Si$_6$O$_9$N$_4$ | | | | | bluish green | |
| | Ba$_3$Si$_6$O$_{12}$N$_2$ | trigonal | P3 | a = 7.5046 c = 6.4703 | | green | |
| | La$_5$Si$_3$O$_{12}$N | hexagonal | P6$_3$/m | a=9.7051 c=7.2546 Z=1 | 591.76 | | white UV>261 |
| | La$_4$SiO$_7$N$_2$ | monoclinic | P12$_1$/C1 | a=8.036 b=10.992 c=11.109 β=110.92 Z=4 | 916.75 | | white UV>283 |
| | LaSiO$_2$N | hexagonal | P6c2 | a=7.310 c=9.550 V=441.95 Z=6 | | | white UV>263 |
| | La$_3$Si$_8$O$_4$N$_{11}$ | orthorhombic | C2/c | a=15.850 b=4.9029 c=18.039 Z=4 | 1271.05 | | white UV>243 |
| | La$_3$[SiON$_3$]O | tetragonal | I4/mcm | a = 6.822, c = 11.074 Å, Z = 4 | | | |
| | La$_{16}$[Si$_8$N$_{22}$][SiON$_3$]$_2$ | triclinic | P1 | a = 5.718, b = 11.391, c = 13.435, α = 112.02, β = 90.19, γ = 90.58 Z=2 | 811.1 | | |
| | Ce$_4$[Si$_4$O$_4$N$_6$]O | | | | | | green-yellow |
| | Ce$_3$[SiON$_3$]O | tetragonal | I4/mcm | a = 6.723, c = 11.069 Å, Z = 4 | | | dark red |
| | Sr$_3$Ce$_{10}$Si$_{18}$Al$_{12}$O$_{18}$N$_{36}$ | | | | | | |
| | Pr$_3$[SiON$_3$]O | tetragonal | I4/mcm | a = 6.6979, c = 11.005 Å, Z = 4 | | | |
| | Pr$_4$Si$_2$O$_7$N$_2$ | | | | | | |
| | Gd$_3$[SiON$_3$]O | tetragonal | I4/mcm | | | | |
| | Sr$_3$Pr$_{10}$Si$_{18}$Al$_{12}$O$_{18}$N$_{36}$ | | | | | | |
| | Sr$_3$Nd$_{10}$Si$_{18}$Al$_{12}$O$_{18}$N$_{36}$ | | | | | | |
| | Sr$_{10}$Sm$_6$Si$_{30}$Al$_6$O$_7$N$_{54}$ | | | | | | |
| | EuSi$_2$O$_2$N$_2$ | triclinic | P1 | a=7.095 b=7.246 c=7.256 α=88.69 β=84.77 γ=75.84 Z=4 | | | |
| ytterbium silicon oxynitride | Yb$_4$Si$_2$O$_7$N$_2$ | | | | | | |