Atomistic origins of the phase transition mechanism in Ge2Sb2Te5

2009 
The fast and reversible phase transition mechanism between crystalline and amorphous phases of Ge2Sb2Te5 has been in debate for several years. Through employing first-principles density functional theory calculations, we identify a direct structural link between the metastable crystalline and amorphous phases. The phase transition is driven by the displacement of Ge atoms along the rocksalt [111] direction from stable octahedron to high energy unstable tetrahedron sites close to the intrinsic vacancy regions, which generates a high energy intermediate phase between metastable and amorphous phases. Due to the instability of Ge at the tetrahedron sites, the Ge atoms naturally shift away from those sites, giving rise to the formation of local-ordered fourfold motifs and the long-range structural disorder. Intrinsic vacancies, which originate from Sb2Te3, lower the energy barrier for Ge displacements, and hence, their distribution plays an important role in the phase transition. The high energy intermediate c...
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