Superionic State in Alumina Produced by Nonthermal Melting

Density functional–based molecular dynamics reveals a transient superionic state in Al2O3 produced by nonthermal phase transition under extreme electronic excitation. At electronic temperatures above Te ≈ 2.75 eV, the oxygen sublattice exhibits fluid behavior, whereas the aluminum sublattice is in a solid state. This state exists up to Te ≈ 3.25 eV, where Al2O3 turns metallic–superionic; at Te ≈ 3.75 eV, the aluminum sublattice disorders. Quenching the superionic state under pressure >400 GPa freezes it into a metastable mixed amorphous–crystalline phase where the oxygen subsystem is disordered solid, whereas the aluminum one is ordered.