Chemical Ordering in Liquid and Supercooled Ge₂Sb₂Te₅ Phase-Change Materials

The origin of chemical ordering in liquid and supercooled liquid Ge₂Sb₂Te₅ (GST) was investigated using ab initio molecular dynamics (AIMD) simulations. Bond dynamics were analyzed via continuous ((Formula presented.)) and intermittent ((Formula presented.)) lifetimes. The intermittent lifetime ((Formula presented.)) reveals that chemically ordered Ge-Te and Sb-Te bonds are the most stable, although (Formula presented.) exhibits a stability anomaly. The faster increase of (Formula presented.) for these bonds upon cooling explains the overall chemical ordering. A novel ordering mechanism was identified through the analysis of bond separation dynamics. Te-Te ‘wrong’ bonds exhibit a unique dynamic instability, breaking and separating much faster than any other bond type, which actively drives the system towards chemical order. A correlation between lifetime and bond strength, as calculated by the Integrated Crystal Orbital Hamilton Population (ICOHP), supports these dynamic findings. Chemical ordering shows a positive correlation with medium-range structural order, evidenced by the instability of 4-fold rings containing wrong bonds. This study provides a detailed dynamic origin for ordering in liquid GST, highlighting the role of Te-Te bond relaxation.