The mechanism of the ultrafast crystal growth of pure metals from their melts

Pure metals can have ultrafast growth rates from their melts, such as a crystal of pure nickel that grows at a rate reaching 70 m s−1. These extraordinary growth rates suggest that metallic crystals might provide the next generation of phase-change materials. The huge crystal growth rates of metals are the consequence of kinetics without activated control, in sharp contrast to the prediction of the ‘classic’ theory of crystal growth. While the existence of barrierless growth kinetics is now well established in atomic melts, the physical explanation for the absence of an activation barrier to ordering remains unclear. It is something of a paradox that diffusion in the liquid metal is governed by thermal activation while the movement of the same atoms organizing into a crystal is not. Here we use computer simulations of crystallization in pure metals to explicitly resolve the origin of the barrierless growth kinetics. Molecular dynamic simulations reveal that the rapid crystal growth in pure metals is governed by a barrierless ordering process, correlating to the inherent crystalline structure in the liquid at the growth interface.