Intercomparison of MgO, Au, Pt pressure standards assessed by NaCl B2 primary pressure scale
Description
Accurate pressure determination is essential to investigate the behaviors of materials under extreme conditions. Despite decades of efforts, it remains a fundamental challenge to establish reliable and interconsistent absolute pressure scales at multi-Mbar conditions as separate calibration studies on same pressure standards as well as cross-calibrations of multiple pressure standards show substantial discrepancies often reaching ~5% at 1 Mbar and ~10% at 3 Mbar. In this study, the elasticity-based primary NaCl B2 pressure scale originally established by Murakami and Takata (2019) is further refined using a modified version of 3rd order Birch-Murnaghan equation of state and fully self-consistent thermodynamic parameters. Thermal pressure effect is calculated for NaCl B2 phase using experimentally-measured thermodynamic parameters at 300 K and Mie‒Grüneisen‒Debye model (MGD) under quasi-harmonic assumption, allowing the thermal EOS of NaCl B2 to be constructed as a reliable primary pressure scale applicable under simultaneous high pressure and temperature conditions. Then, independent high pressure molar volume data (V_MgO,V_Au,V_Pt,V_(NaCl B2)) from published co-compression experiments are reanalyzed to establish secondary MgO, Au, and Pt EOSs using our primary NaCl B2 scale as reference to facilitate intercomparison among these pressure standards/scales as well as to reconcile potential causes of their discrepancies. Finally, our results show that experimental pressures can be determined with a precision better than 2% up to 2 Mbar using a series of independently established and yet mutually consistent primary NaCl B2, MgO, Au and Pt pressure scales.
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Institutions
- ETH ZurichZurich, Zurich