Inherent Simple Cubic Lattice Being Responsible for Ultrafast Solid-Phase Change of Ge2Sb2Te5

Abstract

Crystallization of solid is generally slow in kinetics for atoms trapped in solids. Phase-change materials (PCMs) challenge current theory on its ultrafast reversible amorphous-to-crystal transition. Here by using the stochastic surface walking global optimization method, we establish the first global potential energy surface (PES) for Ge2Sb2Te5. By analyzing all structures on the global PES, we show that an inherent structural pattern of simple cubic lattice is present universally in low-energy structures, either globally in a newly found metastable simple cubic crystal phase or locally in the amorphous structures. Our solid-to-solid reaction pathway sampling reveals that this simple cubic lattice plays a critical role in the rapid amorphous-to-crystal transition, which occurs via dynamic vacancy creation/annihilation, Martensitic-type {100} shearing, and diffusionless local relaxation. This knowledge from global PES allows the prediction of PCMs by linking the phase-change kinetics with the geometry of metastable phases.