Dense pyrite-type crystalline homology in Ultrahigh-pressure silica.

Researchers have measured SiO2 glass to ultra-high pressure of 200 GPa and confronted their results to calculations and found high-coordination can be sustained in silica at such pressures. The results show the formation of OSi4 tetraclusters associated with that of SiO7 polyhedra in SiO2 glass under ultrahigh pressures to 200 gigapascal. Persistent homology analyses with molecular dynamics simulations found increased packing fraction of atoms whose topological diagram at ultrahigh pressures is similar to a pyrite-type crystalline phase, although the formation of tetraclusters is prohibited in the crystalline phase. This critical difference would be caused by the potential structural tolerance in the glass for distortion of oxygen clusters.