317 / 2023-05-04 10:47:06

Distinct Vibrational Signatures and Complex Phase Behavior in Metallic Oxygen

高压物理与材料科学 > 氢与高能量密度材料-II

Pressure is a fundamental thermodynamic tool to probe and tune novel interactions within materials due to the associated reduction in atomic/molecular volumes. This is perhaps most clearly demonstrated by molecular systems, whereby decreasing the distance between molecular units can enhance intermolecular interactions and under sufficient compression can render familiar ambient dielectric gases into metals [1, 2] and/or close packed atomic solids [3, 4]. Evidence for metallization in dense oxygen has been reported for over 30 years [5] at a now routinely accessible 95 GPa [6]. However, despite the longevity of this result and the technological advancements since, the absolute nature of this phase remains poorly constrained [7, 8, 9, 10].



Here, through state-of-art Raman spectroscopy and laser heating we report for the first time, the distinct molecular vibrational character of metallic x-O₂ up to ~150 GPa. Further, we observe and discuss its strong hysteresis and metastability with the precursory phase e(e’)-O₂, which may have resulted in ambiguities in the existing phase diagram of dense oxygen. These findings will reinvigorate experimental and theoretical work into the dense oxygen system, which will have importance for oxygen-bearing chemistries, prevalent in the deep Earth, as well as fundamental physics.

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