Pressure calibration is a central technical challenge of high-pressure research that

1. Pressure calibration is a central technical challenge of high-pressure research that goes hand in hand with experimental advances. Scientific Questions: Transition zone seismic discontinuities – 410, 660 km depth Clapeyron slope – connection to geodynamics Core-Mantle boundary Depth of pPv transition Phase transition vs chemical/thermal boundary Chemical composition (e.g. Fe) Clapeyron slope Triple point, melting curve of H2O Equation of state parameters sensitive to P calibration (e.g. diamond, Fe)

2. What are some things we have learned? Ruby Scale Ruby scale is in need of revision >50 GPa -- definitely 0-50 GPa – perhaps Open Questions Inconsistency of shock standards Can we improve shock thermal corrections? Static studies of Au are not in agreement Emphasizes need for redundancy Details of loading, sample environment may matter Strength of He?

3. Absolute pressure scales from elasticity/volume data highly promising Open questions? Careful analysis of effects of adiabatic/isothermal corrections What is limitation due to our inability to measure K’ to high precision? MgO: K’ = 3.8-4.2 -- 10% uncertainty What are P-T limits of such measurements?

4. Pressure at high temperatures New optical sensors cBN, diamond X-ray markers Thermal equation of state First principles theory, new semi-empirical EOS models Open questions: How accurate are our temperature determinations?

5. Open Questions (contd): Thermal equation of state remains one of the most challenging and unsolved technical questions Within framework of Mie-Gruneisen-Debye EoS: LVP -- sensitive to 0, not q DAC -- Strong tradeoff between K, K’ and q Best functional form of the thermal equation of state? Mie-Gruneisen-Debye Thermodynamic consistency – Gibbs energy Anharmonicity How do we best incorporate first principles theory? Very powerful insights that cannot be obtained from exp. Inherent approximations prevent direct use Simplicity vs Completeness number of parameters: 6-22

6. What do we need to do (both individually and as a community)? Communication and Education Special issue of High-Pressure Research AIRAPT, Shock/Static joint conference COMPRES Main impetus comes from individual investigators Spirit of openness and cooperation Do we need to establish a database of static compression data? examples: Shock compression database, Am. Min. crystal structure database volume, pressure, pressure scale of publication ability to convert data to any other pressure scale for a given standard

7. Proposed experimental program (COMPRES development project?): Fundamental thermoelastic/shock data for simple metals are essential Shock data: mostly obtained in 1950-1970s Ultrasonic elasticity data (K, K’): 1950-1970s Peak pressure: ~1 GPa Bulk Modulus – contrained to better than 1% Pressure derivative of K (K’): >10% variation Example: P derivs. of Cijs for Pt not measured. Project: Program to characterize elasticity of Au, Pt, Mo, Ta, Cu, Al, and Ag at high P and T New elasticity techniques: Impulsive stimulated scattering in DAC Inelastic xray scattering in DAC ultrasonic elasticity in large volume press