Compressibility, Structure, and Melting of Platinum to 500 GPa*

Many high-pressure experiments rely on calibration standards to inform how materials respond under compression.  Platinum is a common pressure standard used in both static and dynamic compression experiments.  Measurement of the crystallographic structure at various pressure–temperature conditions is critical to benchmarking standards such as platinum.  This work reports density and structural data from in situ x-ray diffraction and velocimetry of shocked and ramped platinum.  Different temperature states were accessed by varying the initial shock pressure before further compression along a quasi-isentrope.  The face-centered cubic (fcc) phase was measured up to 480(20) GPa under ramp compression.  Observations of liquid diffraction for platinum shocked to 500 GPa constrain the melting curve on the Hugoniot.  From these results, a melt curve is constructed incorporating previously reported melting measurements. Optical pyrometry provides a lower bound on the Hugoniot melting temperature.