Solid oxygen

Solid oxygen forms at normal atmospheric pressure at a temperature below 54.36 K (−218.79 °C, −361.82 °F). Solid oxygen O₂, like liquid oxygen, is a clear substance with a light sky-blue color caused by absorption in the red part of the visible light spectrum.

Oxygen molecules have attracted attention because of the relationship between the molecular magnetization and crystal structures, electronic structures, and superconductivity. Oxygen is the only simple diatomic molecule (and one of the few molecules in general) to carry a magnetic moment.^[1] This makes solid oxygen particularly interesting, as it is considered a "spin-controlled" crystal^[1] that displays antiferromagnetic magnetic order in the low temperature phases. The magnetic properties of oxygen have been studied extensively.^[2] At very high pressures, solid oxygen changes from an insulating to a metallic state;^[3] and at very low temperatures, it even transforms to a superconducting state.^[4] Structural investigations of solid oxygen began in the 1920s and, at present, six distinct crystallographic phases are established unambiguously.

The density of solid oxygen ranges from 21 cm³/mol in the α-phase, to 23.5 cm³/mol in the γ-phase.^[5]