Melting behavior and dynamical properties of Cr2Ge2Te6 phase-change material

TL;DR

This study uses ab initio molecular dynamics to explore the melting and dynamical behavior of Cr2Ge2Te6, revealing how atomic structures evolve and remain stable at high temperatures, informing phase-change memory performance.

Contribution

It provides detailed insights into the melting process and structural stability of Cr2Ge2Te6, a promising phase-change material, through advanced simulations.

Findings

Ge atoms leave lattice sites earlier than Cr and Te during heating.

Cr[Te6] octahedra remain stable up to 1400 K.

Supercooled liquid CrGT retains most Cr octahedra, facilitating rapid crystallization.

Abstract

Cr2Ge2Te6 (CrGT) is known as an intrinsic ferromagnetic semiconductor and a promising candidate for phase-change memory applications. In amorphous CrGT, Cr atoms form non-defective octahedral motifs with Te atoms, similar to those in the crystalline phase. The abundance of Cr[Te6] octahedra is regarded as the key structural factor in reducing the resistance drift coefficient of amorphous CrGT. However, the stage at which these octahedra emerge during melt-quench amorphization remains unclear. Here, we present ab initio molecular dynamics (AIMD) simulations to model the melting process of crystalline CrGT and to investigate the dynamical properties of liquid and supercooled liquid CrGT in detail. Upon heating, Ge atoms are observed to leave their lattice sites earlier than Cr and Te atoms, diffusing into the van der Waals gap and initiating the collapse of the layered structure. The Cr[Te6] octahedra are more robust, maintaining their structural pattern up to 1400 K despite continuous rupture and re-formation of Cr-Te bonds. At higher temperatures, Cr and Te atoms start to migrate independently. In supercooled liquid CrGT at 550 K, most Cr-centered octahedra remain intact, with only limited Cr-Te bond breaking. The collective motion of these octahedra in this temperature regime helps explain why crystallization in CrGT devices can be accomplished in tens of nanoseconds.