for solid oxygen Six different
phases of solid oxygen are known to exist: • α-phase:
light blue forms at 1 atm, below 23.8 K,
monoclinic crystal structure,
space group C2/
m (no. 12). • β-phase:
faint blue to
pink forms at 1 atm, below 43.8 K, rhombohedral crystal structure, space group
Rm (no. 166). At room temperature and high pressure begins transformation to tetraoxygen. • γ-phase:
faint blue forms at 1 atm, below 54.36 K, cubic crystal structure,
Pmn (no. 223). • δ-phase:
orange forms at room temperature at a pressure of
9 GPa • ε-phase:
dark-red to
black forms at room temperature at pressures greater than 10 GPa • ζ-phase:
metallic forms at pressures greater than
96 GPa 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. However, this is a different
allotrope of oxygen, , not merely a different crystalline phase of O2.
Metallic oxygen A ζ-phase appears at 96 GPa when ε-phase oxygen is further compressed. exhibits superconductivity at pressures over 100 GPa and a temperature below 0.6 K. == References ==