title: Polymorphism of dense, hot oxygen.
abstract: The phase diagram and polymorphism of oxygen at high pressures and temperatures are of great interest to condensed matter and earth science. X-ray diffraction and Raman spectroscopy of oxygen using laser and resistively heated diamond anvil cells reveal that the molecular high-pressure phase ε-O(2), which consists of (O(2))(4) clusters, reversibly transforms in the pressure range of 44 to 90 GPa and temperatures near 1000 K to a new phase with higher symmetry. The data suggest that this new phase (η') is isostructural to a phase η reported previously at lower pressures and temperatures, but differs from it in the P-T range of stability and type of intermolecular association. The melting curve increases monotonically up to the maximum pressures studied (∼60 GPa). The structure factor of the fluid measured as a function of pressure to 58 GPa shows continuous changes toward molecular dissociation.
authors: Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015, USA. goncharov@gl.ciw.edu
authors: Alexander F
authors: AF
authors: Goncharov
authors: N
authors: N
authors: Subramanian
authors: T R
authors: TR
authors: Ravindran
authors: Maddury
authors: M
authors: Somayazulu
authors: Vitali B
authors: VB
authors: Prakapenka
authors: Russell J
authors: RJ
authors: Hemley