The thermodynamics of several elements at high pressure

We have used the CALPHAD-compatible equation of state (EOS) based on the explicit Gibbs free energy concept for the solid state of ten important elements: V, Nb, Ta, Mo, W (groups VB and VIB), Pd, Pt (group VIIIB) and Cu, Ag and Au (group IB). The new formulation uses SGTE data for ambient pressure and converges to the quasi-harmonic model at the limit of extreme pressure to calculate the Gibbs free energy as a function of pressure and temperature. The model is based on the available pressure–volume–temperature ( P V T ) data on the elements and can be usefully extrapolated to extreme pressures. When compared to shock wave data, the modeled EOS holds well, but the fit is not totally satisfactory in the ultrahigh-pressure range. A great advantage of this formulation is that it can be used to calculate thermodynamic properties such as the heat capacity and entropy at very high temperatures and pressures.