Evaluation of Pt and Au pressure scales based on MgO absolute pressure scale

The equations of state(EOSs)of MgO produced by two independent scale-free methods,(1)the simultaneous elastic wave velocity and in situ synchrotron X-ray measurements(Kono et al.,2010;Li et al.,2006)and(2)the first-principles calculations(Wu et al.,2008),agree well with each other to at least 150 GPa and 2000 K.Furthermore,the EOS from first-principles calculations also agrees well with shock wave data,another pressure-scale-free data.These agreements strongly support that these EOSs provide reliable absolute pressure scales.Here we evaluate Au and Pt EOSs based on the EOS of Wu et al.(2008)using the simultaneously measured volume data of MgO,Au,and Pt from the literature.The primary pressure scales developed by Tange et al.(2009)and Yokoo et al.(2009)using only pressure-scale-free experimental data of MgO,Au,and Pt produce internal consistent pressure and agree with EOS of Wu et al.(2008).The Au EOS by Tsuchiya(2003)works well at room temperature but underestimates pressure at high temperature.The Au EOS by Fei et al.(2007)can well describe thermal pressure.The EOSs of Pt by Holmes et al.(1989)and Ono et al.(2011)work well at both room temperature and high temperature.The results also suggest that the discrepancy between bulk modulus of iron from experiments(Mao et al.,1990)and those from Earth's core(Dziewonski and Anderson,1981)is not originated from the overestimation of pressure by the EOS of Holmes et al.(1989).At high pressure and temperature,pressure uncertainty resulted from volume error becomes similarly important as the accuracy of the pressure scale.