HPCAT Workshop on Advances in Matter Under Extreme Conditions, Oct. 11-12, 2012

1. Break out Session Structure, bonding, and thermodynamic properties reaching 0.5 TPa and beyond Co-chairs: Tom Duffy (Princeton), Stan Bonev (LLNL) Panelists: ReinhardBoehler (Carnegie), Brent Fultz (Caltech), Carl Greef (LANL), Eugene Gregoryanz (Edinburgh), Richard Scalettar (UC Davis), Alex Navrotsky (UC Davis) HPCAT Workshop on Advances in Matter Under Extreme Conditions, Oct. 11-12, 2012

2. Priority Research Directions • Ultrahigh Pressure Frontier (0.5 TPa and beyond) • Bridging the strain rate gap between static and dynamic experiments • Thermodynamics and kinetics at high P-T conditions • Complex, heterogeneous materials • Elasticity, strength, and rheology at Mbar pressures

3. Ultrahigh Pressure Frontier (Beyond 2 Mbar) • Scientific Challenges • --Wide open for exploration; Terra Incognito for phase transitions, thermodynamics, bonding, and structures • --Hydrogen above 300 GPa • -- Reaching conditions of the Center of the Earth • --Interior structure of SuperEarths • Wide range of compositions: H2, He, ices, silicates, iron alloys, carbon, carbides etc. • -- Single crystal diffraction at multimegabar conditions • --More complex materials and multi-phase assemblages

4. Is Hydrogen Metallic above 250 GPa

5. How accurate (meaningful) are temperature measurements ? role of diamond distortion Tateno et al. Science 2010 • Need to reach up to 3.6 Mbar and 6000 K under well controlled conditions

6. Key Questions About Planets Inside and Outside the Solar System Sanchez-Lavega, 06 • What are the interior structures of Jupiter, Neptune and the other giant planets? • What is the nature of cores of terrestrial planets? • What kinds of planets exist outside our solar system? Can we characterize their structure, composition, dynamics and evolution? • How do different types of planetary systems form and what are the implications for the origin and evolution of solar systems?

7. Ultrahigh Pressure Frontier (Beyond 2 Mbar) • Technical Challenges • --At present, measuring anything above 2 Mbar is difficult • ---- New anvil designs: Multi-stage anvils, Multi-carat single crystal CVD diamond, Nano polycrystalline diamond, designer anvils • --Submicron x-ray beam • --Characterizing pressures, temperatures, stresses • --High sensitivity measurement techniques due to very small sample volumes. A major effort in this area could have large payoff.

8. Sciences at Static Pressures above 300 GPa Technical Challenges • New methods are needed to reproducibly and consistently generate static pressures above 300 GPa: e.g. double stage diamond anvil cell Dubrovinskaya et al., 640 GPa on metals. Shown at GRC and EHPRG 2012

9. Phase Diagrams at High P and T High P (> 0.5 TPa) means high T. Generally good consistency among dynamic measurements. Most theory in general agreement with dynamic data. High temperatures are very technically challenging for static.

11. 2. Bridging the strain rate gap between static and dynamic experiments • (HPCAT- DCS synergy) • Scientific Challenges • --Large difference in strain rate between traditional static and dynamic (shock) experiments leaves many open questions • Rate dependence of phase transformations, mechanical properties, deformation behavior • --Dynamic experiments lack structural diagnostics (i.e., X-ray diffraction) • --Example: SiO2. Decades of dynamic experiments have documented a complex phase transition from low-density silica phases (e.g. quartz) to dense high-pressure phase (“stishovite-like”) with complicated transition pathway, metastabilityand kinetic effects . Relevant to many other silicates as well. • Impact phenomena and shock processes are of major importance in materials science, geophysics and planetary science

12. 2. Bridging the strain rate gap between static and dynamic experiments • (HPCAT- DCS synergy) • Technical Challenges • --Development on new time resolved techniques over a range of time scales • --Theoretical models of thermodynamic and constitutive behavior across orders of magnitude change in strain rate • --Need to develop different probes to interrogate materials across different timescales • --Unique opportunity to bring together expertise in dynamic compression with expertise in X-ray techniques

13. Thermodynamics and kinetics at high P-T: • Scientific Challenges: • Phase transitions, crystal structures, and thermodynamics are and will likely remain the dominant focus of most user groups at HPCAT • How does the thermodynamics of solids change under pressure and temperature? • Anharmonic theory by perturbation methods needs to be extended, or better results need to be extracted from molecular dynamics methods • Pressure as a probe of kinetic processes; What can pressure tell us about transition states of charge or ion transport in crystals? • Technical Challenges: • Developments in techniques in inelastic X-ray scattering; couple to other techniques outside HPCAT (spectroscopic techniques, neutron diffraction) • Improved characterization of a range of P-T states (thermal expansivity, melting , dynamics); Better standards for pressure and temperature characterization • Databases of thermodynamic functions for high P-T conditions; Developments and advances in theory coupled with experiments (e.g. strongly correlated materials)

14. 4. Complex, heterogeneous materials across a range of P-T Conditions • Scientific Challenges • Studies of nanophase, disordered, amorphous and liquid mateirals • Phase relationships and elemental partitioning in MgO-FeO-Al2O3-SiO2 system at 100-150 GPa and >2000 K • Understanding the complex behavior of Fe in mantle silicates: valence state, spin state, and site variation • inhomogeneitiesand their possible role in transport and thermodynamics/phase transitions.  Example: effects of inhomogeneities on antiferromagnetic order and superconductivity in high Tc superconductors

15. Complex, heterogeneous materials across a range of P-T Conditions Technical Challenges Combine well-established structural probes with developing chemical probes to fully characterize the micro- or nano-scale sample environment Pair Distribution Functions/Total X-ray Scattering methods as a function of pressure and temperature is a very powerful tool to study the changes in the atomic structure of crystalline, nano-crystalline and amorphous materials; determine structure on both local and intermediate lengthscales Studies of liquids especially needed Can we bring back the materials we make (either stable or metastable) ? What determines whether a high-pressure phase is quenchable? How can we recover large samples?

16. Elasticity, strength, and rheology at megabarpressures • Scientific Challenges • --Fundamentally important but poorly characterized properties • --Essential for optimizing high-pressure devices, modeling structure and dynamics of Earth’s interior, and for interrelating static and dynamic experiments • --Understanding hard materials (e.g carbides, nitrides) at ultrahigh P • Technical Challenges • --Need higher precision techniques for single-crystal and aggregate elastic properties, especially shear modulus, that can reliably reach higher pressures and temperatures • --New methods for enhanced rheological measurements especially at high T conditions. • --Applications to a wider range of materials, development of databases, integrated understanding from theory and experiment