| Abstract Scope |
Almost four decades ago, a phenomenon called amorphous-amorphous transition (AAT) was first observed in ice under pressure and later in other materials such as silicon. However, the nature of AAT remains highly debated. We used a state-of-the-art machine-learning potential and local structural analysis to investigate the microscopic kinetics of AAT in silicon after a rapid pressure change. We found that the transition from low-density-amorphous (LDA) to high-density-amorphous (HDA) occurs through nucleation and growth, resulting in non-spherical interfaces that underscore the mechanical nature of AAT. In contrast, the reverse transition occurs through spinodal decomposition. Further pressurization transforms LDA into very-high-density amorphous (VHDA), with HDA serving as an intermediate state. Notably, the final amorphous states are inherently unstable, transitioning into crystals. Our findings demonstrated that AAT and crystallization are driven by joint thermodynamic and mechanical instabilities, assisted by preordering, occurring without diffusion. This work was published in [Nat. Commun. 15, 368 (2024)]. |