First-principles simulations of local structure contrast for liquid Ge1Sb2Te4, Ge2Sb2Te5, and Ge4Sb1Te5 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: Ge1Sb2Te4, Ge2Sb2Te5, and Ge4Sb1Te5. In long timescale mean square displacements (MSD), we observe that the element coupled state for Ge1Sb2Te4 and Ge2Sb2Te5 is significantly better than that of Ge4Sb1Te5. The careful analyses by pair correlation functions (PCF) and compositional disorder numbers (CDN) show that Ge2Sb2Te5 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 90 degrees bond angle. The present results are helpful to understand the rapid storage technique based on Ge-Sb-Te alloys. (c) 2012 Elsevier B.V. All rights reserved.