Cobalt(II,III) oxide

Cobalt(II,III) oxide is an inorganic compound with the formula Co3O4. It is one of two well characterized cobalt oxides. It is a black antiferromagnetic solid. As a mixed valence compound, its formula is sometimes written as CoIICoIII2O4 and sometimes as CoO•Co2O3.

Structure
Co3O4 adopts the normal spinel structure, with Co2+ ions in tetrahedral interstices and Co3+ ions in the octahedral interstices of the cubic close-packed lattice of oxide anions.

Synthesis
Cobalt(II) oxide, CoO, converts to Co3O4 upon heating at around 600–700 °C in air. Above 900 °C, CoO is stable. These reactions are described by the following equilibrium:
 * 2 Co3O4   6 CoO  +  O2

Applications
Cobalt(II,III) oxide is used as a blue coloring agent for pottery enamel and glass, as an alternative to cobalt(II) oxide.

Cobalt(II,III) oxide is used as an electrode in some lithium-ion batteries, possibly in the form of cobalt oxide nanoparticles.

Safety
Cobalt compounds are potentially poisonous in large amounts.