Polymorphism of gold under laser-based ramp compression to 690 GPa

The high-pressure behavior and polymorphism of gold have attracted strong recent interest from theory as well as from both static and dynamic experiments. In this study, gold was dynamically ramp-compressed to 690 GPa via laser ablation using the Omega Laser Facility (University of Rochester) in order to investigate the stability regions of this noble metal's polymorphs. Stresses were determined from measurements of surface or interface velocities by laser interferometry. In situ x-ray diffraction was carried out to constrain the structure and density. The ambient face-centered-cubic (fcc) phase was observed at 162 GPa, followed by a mixed-phase region consisting of the fcc and body-centered-cubic (bcc) phases. The presence of only the bcc phase was observed between 377 and 690 GPa. Our results are consistent with recent shock-compression experiments and demonstrate that gold transforms to the bcc phase under conditions of both ramp and shock loading.