Single-crystal X-ray diffraction study of O2 up to 200 GPa

As an archetypal molecular system, oxygen is one of the most studied elements at high pressures and features a surprisingly complex solid-state behavior. Stable from 10 GPa, the ε-O2 phase is comprised of exotic (O2)4 units, and transforms into the ζ-O2 polymorph above 96 GPa. Observed up to the highest pressure attained on oxygen, 134 GPa, this molecular, metallic, and superconducting phase is of the utmost importance for fundamental condensed matter physics and earth sciences. Even though the crystal structure of ζ-O2 is a prerequisite for its understanding, it could not be refined due to insufficient data quality. In this proposal, single-crystal X-ray diffraction of polycrystalline samples (SC-XRDp), coupled with the EBS-ESRF fuelled ID27 beamline's exceptional capabilities, will be employed to unambiguously solve the crystal structure of ζ-O2 and unveil the phase diagram of oxygen up to 200 GPa.