First-principles simulations of local structure contrast for liquid Ge ₁Sb ₂Te ₄, Ge ₂Sb ₂Te ₅, and Ge ₄Sb ₁Te ₅ alloys

Ge-Sb-Te alloys have played a critical role in present nonvolatile optical and electrical storages. It is generally accepted that their "data encoding" (i.e. amorphization) needs the crystal melting and subsequent quenching. Therefore, liquid should be an important intermediate state during the storage. In this study, based on first-principles molecular dynamics we compared the structural properties of liquid Ge-Sb-Te alloys with three compositions: Ge ₁Sb ₂Te ₄, Ge ₂Sb ₂Te ₅, and Ge ₄Sb ₁Te ₅. In long timescale mean square displacements (MSD), we observe that the element coupled state for Ge ₁Sb ₂Te ₄ and Ge ₂Sb ₂Te ₅ is significantly better than that of Ge ₄Sb ₁Te ₅. The careful analyses by pair correlation functions (PCF) and compositional disorder numbers (CDN) show that Ge ₂Sb ₂Te ₅ has the best stability among the three liquids. Bond angle distributions (BAD) further reflect that all the three liquids essentially retain the crystalline character of local structure with 90̊ bond angle. The present results are helpful to understand the rapid storage technique based on Ge-Sb-Te alloys.