Simultaneous volume measurements of Au and MgO to 140 GPa and thermal equation of state of Au based on the MgO pressure scale

We have determined the unit-cell volumes of Au and MgO by synchrotron X-ray diffraction (XRD) measurements at pressures between 11 and 140 GPa and temperatures from 300 to 2330 K in a diamond-anvil cell (DAC). Since the MgO pressure scale appears the most practical at present, it is useful to obtain the P–V–T equation of state of Au that is consistent with the MgO scale. Here we present the new Au pressure scale based on the simultaneously measured volume data of Au and MgO in this study and in Fei et al. [Fei, Y., Li, J., Hirose, K., Minarik, W., Van Orman, J., Sanloup, C., Westrenen, W.V., Komabayashi, T., Funakoshi, K., 2004. A critical evaluation of pressure scales at high temperatures by in situ X-ray diffraction measurements. Phys. Earth Planet. Inter. 143–144, 515–526] using MgO as a reference pressure scale. The new scale predicts larger thermal pressure than previously proposed thermal equations of state of Au and therefore gives higher pressure above 1500 K in a pressure range exceeding 35 GPa.