Ultrahigh-pressure scales for gold and platinum at pressures up to 550 GPa

Abstract

Equation of state of gold (Au) is revised using the remeasured shock compression data at pressures up to 580 GPa with including the electronic free-energy contribution. The model, even though determined only using pressure-scale-free data, can reproduce not only the shock compression data but also the zero-pressure thermodynamic properties with remarkable accuracy. Previous models for the EOS of copper, silver, and MgO that were constructed using as a basis old shock compression data are found to underestimate the pressure seriously (up to $\ensuremath{\sim}12%$ at 200 GPa and 300 K). Moreover, we redetermine the EOS model of platinum (Pt) through the same procedure. The determined models of Au and Pt are found mutually highly consistent, which provide quite comparable pressure values in extensive $P$, $T$ range. These are expected to be more reliable primary pressure standards than previous models.