Growth mechanisms of body-centered cubic and quasi-crystalline Ta

Compared with the growth of periodic crystals, the growth of aperiodic quasi-crystals remains elusive in many respects, particularly regarding their underlying growth mechanisms. Here, we perform molecular dynamics simulations to investigate the growth behavior of the body-centered cubic phase and the quasi-crystalline metastable phase in tantalum (Ta). The results show that both phases can be described by a diffusion-limited growth model, yet they exhibit fundamentally distinct atomistic mechanisms. The crystalline phase grows via a continuous mechanism, in which atoms can simultaneously propagate across multiple unit cells on a rough interface. In contrast, the quasi-crystalline metastable phase grows through a screw dislocation-mediated mechanism on a smooth interface, where atomic attachment is restricted to approximately a single unit cell. As a result, the growth rate of quasi-crystals is several times slower than that of crystals under comparable conditions. The distinct growth mechanisms of crystals and quasi-crystals are closely related to the type and characteristics of the locally ordered atomic species at their respective interfaces. These findings offer new physical insights into the correlation between crystal and quasi-crystal growth mechanisms and provide a fresh perspective on the underlying origin of the remarkable glass-forming ability of elemental Ta.