The cross-calibrated equations of state of gold and platinum measured above 4 Mbar in the toroidal diamond anvil cell*

Characterizing complex high pressure-temperature phenomena in physics, chemistry, and Earth and planetary sciences hinges on the accuracy of the experimental pressure calibrant. Recently, novel diamond-anvil designs have allowed for the routine compression of materials to pressures greater than 300 GPa. At these extreme conditions, equations of state of common pressure calibrants including gold, platinum, KCl, and NaCl have not been extensively calibrated across both static and dynamic data. Here we report pressure-volume-temperature (P-V-T) data for these materials collected in a newly designed toroidal diamond anvil cell to 420 GPa. We measured the unit-cell volumes of Pt, Au, and Re simultaneously in the diamond cell at room temperature. The 300 K equation of state of cross-calibrated platinum and gold corrected for uniaxial stress using line-shift analysis will be compared to recent static and ramp compression data. We then compressed Pt in KCl and NaCl and laser heated the samples at ultra-high pressures. Thermal equation of state data for Pt in the alkali halide media will be compared to the nonhydrostatic data, and the high P-T structural properties of Pt will be reported.