Transition of strong, wide band-gap oxide insulators to metallic glasses at 100 GPa (Mbar) pressures, etc

Abstract

This paper is a review of experimental results observed for shock and statically compressed sapphire (single-crystal Al2O3) and implications of these results. Many of these were unexpected prior to experiments: (i) Hugoniot and 300-K theoretical isotherm are nearly coincident to 340 GPa, (ii) shock-compressed sapphire probably achieves minimum metallic conductivity (MMC) at ~300 GPa, as does fluid H at 140 GPa, (iii) Both crossovers are driven by shock dissipation and both probably occur by a bonds to bands transition (BtBT), (iv) the BtBT is driven by shock-induced damage which breaks bonds at such high densities that wave functions of atoms so formed hybridize into energy bands; (v) disorder caused by sluggish phase transitions in a DAC suggest sapphire also reaches MMC in a DAC at ~300 GPa; (vi) the structural ground states of all solids at very high pressures might be metallic glasses; (vii) Super Earths can have magnetic fields caused only by convecting conducting oxides without the need for Fe; (viii) alumina powders in a DAC might attain MMC at ~300 GPa and perhaps at pressures as low as ~200 GPa. Al2O3 is probably amorphous in a DAC at 200 GPa