Intercomparison of the gold, platinum, and MgO pressure scales up to 140 GPa and 2500 K

Abstract

In order to intercalibrate the equations of state (EOSs) of the three widely used pressure standards, gold, platinum, and MgO, we have measured their unit cell volumes together in the laser‐heated diamond anvil cell up to 140 GPa and 2500 K. At 300 K, three standards agree with each other within ±2.5 GPa to 135 GPa if the EOSs measured in quasi‐hydrostatic media are used. We further refined the EOSs at 300 K, making them consistent with each other within ±1 GPa up to 135 GPa. At high temperature (T), the three standards match the best within ±1 GPa between 40 and 140 GPa, when we use the scales by Dorogokupets and Dewaele (2007). However, a 2–3 GPa discrepancy remains at 20–40 GPa and 1500–2000 K, with gold yielding the highest pressure (P). The pressure discrepancy is likely related to steep decreases in the Grüneisen parameter, the anharmonicity, and/or the electronic effects for the standards at the P‐T conditions. Because gold melts near the temperatures expected for the mantle transition zone, severe anharmonic effects expected under premelting conditions make gold unsuitable for determining the phase boundaries in the region. The pressure scales by Dorogokupets and Dewaele (2007) provide tighter constrains on the Clapeyron slopes of the postspinel boundary to −2.0 to −2.7 MPa/K and the postperovskite boundary to 7–10 MPa/K. The data and refined EOSs presented here allow for reliable comparisons among experiments with different pressure standards for the entire P‐T conditions expected for the Earth's lower mantle.

The Bridgmanite–Akimotoite–Majorite Triple Point Determined in Large Volume Press and Laser-Heated Diamond Anvil Cell

“…Pt, Au, and MgO could be good candidates as they have been used widely in LHDAC. However, despite the agreements over a larger pressure range, the MgO, Au, and Pt scales by Dorogokupets and Dewaele [29] are different by ∼2 GPa at 20-40 GPa and high temperatures according to Ye et al [11]. Therefore, an important challenge still remains for the thermal EOS of important materials at the pressure range for the mantle transition zone.…”

“…For our LHDAC experiments, we chose to use the thermal EOS of Pt by Dorogokupets and Dewaele [29]. This pressure scale is known to yield better agreements with the Au and MgO scales according to Ye et al [11] for a wide pressure range. In order to ensure the consistency between LHDAC and LVP results, it would be useful to examine the agreements between the W scale and the Pt scale at in situ high P−T.…”

“…However, early experiments found that results from different pressure scales and different experimental techniques differed by 2-3 GPa for the important phase boundaries near the 660-km discontinuity [2][3][4][5][6]. Intense efforts have been made since then [7][8][9], but the discrepancy for some important phase boundaries still remain unresolved [10,11]. Other potential sources of the discrepancy have been investigated.…”

Phase transformation of hydrous ringwoodite to the lower-mantle phases and the formation of dense hydrous silica

“…S4 (Prescher and Prakapenka, 2015). We performed phase 112 identification and peak fitting in the PeakPo package (Shim 2017). The data obtained 113 from the GSECARS and the 12.2.2 beamlines agreed well with each other.…”

“…Pressure was measured 88 using the ruby fluorescence line shift or the first-order Raman mode from the tips of the 89 diamond anvils (Mao et al, 1978). For the NIR measurements, we mixed the Rw starting 90 material with 10 wt% Pt, the latter being used as a laser coupler and internal pressure 91 standard when using XRD (Ye et al 2017). We loaded Ne as a pressure medium using 92 the gas-loading system at the GESCARS, APS.…”