Unravelling the Mechanism of Pressure Induced Amorphization of Phase Change Materials

Based on ab initio molecular dynamics simulations, we identify the atomistic mechanism of the pressure induced amorphization of ${\mathrm{Ge}}_2{\mathrm{Sb}}_2{\mathrm{Te}}_5$. The simulations reveal that homopolar $\mathrm{Ge}/\mathrm{Sb}$ bonds appear in cubic ${\mathrm{Ge}}_2{\mathrm{Sb}}_2{\mathrm{Te}}_5$ under pressure, giving rise to square rings rotated by 45° with respect to the crystalline axis whose formation is induced by the displacement of Te atoms filling the voids of neighboring $\mathrm{Ge}/\mathrm{Sb}$ stoichiometric vacancies. The concentration of these topological defects increases with pressure up to 21 GPa at which the system is destabilized and transforms into an amorphous phase in agreement with experiments.