Metallic liquid hydrogen and likely Al2O3 metallic glass

TL;DR

This paper discusses the synthesis of liquid metallic hydrogen at high pressure and predicts Al2O3 might become a metallic glass at even higher pressures, with implications for planetary science.

Contribution

It presents experimental and theoretical insights into metallization mechanisms in hydrogen and Al2O3 under extreme pressures, proposing a Mott-like transition as the key process.

Findings

Liquid metallic hydrogen synthesized at 140 GPa.

Al2O3 predicted to become a metallic glass at ~300 GPa.

Shock dissipation behavior changes above 400 GPa.

Abstract

Dynamic compression has been used to synthesize liquid metallic hydrogen at 140 GPa (1.4 million bar) and experimental data and theory predict Al2O3 might be a metallic glass at ~300 GPa. The mechanism of metallization in both cases is probably a Mott-like transition. The strength of sapphire causes shock dissipation to be split differently in the strong solid and soft fluid. Once the 4.5-eV H-H and Al-O bonds are broken at sufficiently high pressures in liquid H2 and in sapphire (single-crystal Al2O3), electrons are delocalized, which leads to formation of energy bands in fluid H and probably in amorphous Al2O3. The high strength of sapphire causes shock dissipation to be absorbed primarily in entropy up to ~400 GPa, which also causes the 300-K isotherm and Hugoniot to be virtually coincident in this pressure range. Above ~400 GPa shock dissipation must go primarily into temperature, which is observed experimentally as a rapid increase in shock pressure above ~400 GPa. The metallization of glassy Al2O3, if verified, is expected to be general in strong oxide insulators. Implications for Super Earths are discussed.