oxynitride

Oxynitride is a class of compounds that contain both oxide and nitride ions in the same crystal lattice. They are a type of mixed-anion material, formed by partially substituting nitrogen for oxygen in oxides or by incorporating nitrogen into nitride frameworks. The term encompasses crystalline solids, as well as oxynitride glasses and ceramics.

Prominent examples include aluminum oxynitride (ALON), a transparent ceramic used for protective windows and armor applications; silicon oxynitride materials used in optical coatings and waveguides; and ternary oxynitrides such as LaTiO2N, a perovskite-type compound studied for visible-light photocatalysis. The properties often depend on how O2− and N3− ions are arranged in the lattice.

Structure and properties: Mixed oxide–nitride anions create tunable band gaps, refractive indices, and hardness. Depending on composition, oxynitrides can be insulators, semiconductors, or dielectric materials. Some oxynitride ceramics exhibit high chemical stability and thermal resistance, while others serve as functional materials in optics or energy conversion.

Synthesis: Oxynitrides are typically prepared by ammonolysis or nitridation of oxides, or by combining metal sources with nitrogen and oxygen donors at high temperatures. Other methods include chemical vapor deposition, sputtering, and sol–gel routes that incorporate nitrogen during gel formation. Post-synthesis annealing can influence anion distribution and phase behavior.

Applications and outlook: Oxynitrides are investigated for protective optics, transparent armor, and coatings, as well as for photocatalysis and photoelectrochemical devices. Ongoing research explores tuning the composition and structure to optimize optical, electronic, and catalytic properties across a range of temperatures.