Solid oxygen

[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.

[4] Structural investigations of solid oxygen began in the 1920s and, at present, six distinct crystallographic phases are established unambiguously.

[5] Six different phases of solid oxygen are known to exist:[1][6] It has been found that oxygen is solidified into a state called the β-phase at room temperature by applying pressure, and with further increasing pressure, the β-phase undergoes phase transitions to the δ-phase at 9 GPa and the ε-phase at 10 GPa; and, due to the increase in molecular interactions, the color of the β-phase changes to pink, orange, then red (the stable octaoxygen phase), and the red color further darkens to black with increasing pressure.

It was found that a metallic ζ-phase appears at 96 GPa when ε-phase oxygen is further compressed.

[6] As the pressure of oxygen at room temperature is increased through 10 gigapascals (1,500,000 psi), it undergoes a dramatic phase transition.