Atomistic origins of the phase transition mechanism in Ge2Sb2Te5

TL;DR

This study uncovers the atomistic mechanism behind the phase transition in Ge2Sb2Te5, revealing how Ge atom displacements and vacancy regions facilitate the switch between crystalline and amorphous phases, crucial for phase-change memory applications.

Contribution

It provides a detailed first-principles analysis linking atomic displacements to phase transition pathways in Ge2Sb2Te5, highlighting the role of vacancies and tetrahedral site instability.

Findings

Ge atom displacement along [111] drives phase change

Tetrahedral site instability facilitates amorphization

Intrinsic vacancies enhance phase transition efficiency

Abstract

Combined static and molecular dynamics first-principles calculations are used to identify a direct structural link between the metastable crystalline and amorphous phases of Ge2Sb2Te5. We find that the phase transition is driven by the displacement of Ge atoms along the rocksalt [111] direction from the stable-octahedron to high-energy-unstable tetrahedron sites close to the intrinsic vacancy regions, which give rise to the formation of local 4-fold coordinated motifs. Our analyses suggest that the high figures of merit of Ge2Sb2Te5 are achieved from the optimal combination of intrinsic vacancies provided by Sb2Te3 and the instability of the tetrahedron sites provided by GeTe.