On the structure of high-pressure high-temperature eta-O2

In situ high-pressure high-temperature x-ray diffraction and optical studies have been conducted on solid oxygen between 10 and 20 GPa and up to 700 K. Optical observations and Raman spectroscopic studies have been utilized to confirm the existence of β -O2 and to identify phase behavior and phase boundaries of Β -, ε - and η -O2 at elevated temperatures. Subsequent single-crystal synchrotron x-ray diffraction studies yielded the structure of the η -O2 phase at 15.9 GPa and 625 K.