SnO2

Tin(IV) oxide, SnO2, is an inorganic compound that appears as a white solid. In nature it occurs as cassiterite, the main ore of tin. It is widely used as a wide-band-gap n-type semiconductor with a band gap near 3.6 eV and is processed in powder or thin-film forms for various technologies.

The material crystallizes in the rutile structure, a tetragonal arrangement in which Sn4+ ions occupy sixfold coordinated sites with oxygen. The intrinsic n-type conductivity of SnO2 is largely due to oxygen vacancies, which donate free electrons. Doping with aliovalent cations further increases carrier concentration and decreases resistivity, enabling practical electronic and optoelectronic applications. In thin films, SnO2 can be made optically transparent in the visible range while remaining electrically conductive.

Doped tin oxide variants are common, notably antimony-doped tin oxide (ATO) and fluorine-doped tin oxide (FTO). These materials are widely used as transparent conducting oxides (TCOs) in displays, solar cells, and other optoelectronic devices, where a balance of transparency and conductivity is required.

Applications extend beyond electronics. SnO2 serves as a sensing material in metal-oxide semiconductor gas sensors that detect reducing and oxidizing gases (such as CO, H2, CH4, and NOx) by changes in electrical resistance upon gas adsorption. It also functions as a catalyst support and as a component in various catalytic and environmental technologies.

Synthesis methods include precipitation, sol-gel processing, chemical vapor deposition, sputtering, and spray pyrolysis, producing powders or thin films with tailored microstructures and dopant levels.