Effects of pressure on atomic and electronic structure and crystallization dynamics of amorphousGe2Sb2Te5

Abstract

We investigate the effects of pressure on atomic and electronic structures of amorphous ${\text{Ge}}_{2}{\text{Sb}}_{2}{\text{Te}}_{5}$ using first-principles methods. The supercell volume is varied from 0.94 to 1.13 times the nominal amorphous volume in melt-quench simulations. When the simulation cell is compressed, we find that the energy gap is reduced and the number of localized in-gap states is increased. These results indicate that pressurized amorphous ${\text{Ge}}_{2}{\text{Sb}}_{2}{\text{Te}}_{5}$ exhibits better conduction than ${\text{Ge}}_{2}{\text{Sb}}_{2}{\text{Te}}_{5}$ formed under stress-free conditions. We also find that the positive pressure increases the densities of fourfold rings in amorphous ${\text{Ge}}_{2}{\text{Sb}}_{2}{\text{Te}}_{5}$, shifting the local order toward the crystalline phase. Consistently, fast crystallization is identified for compressed amorphous ${\text{Ge}}_{2}{\text{Sb}}_{2}{\text{Te}}_{5}$.