Local structural signs for distinct crystallization behaviors of monatomic metals

The competition between crystallization and vitrification is crucial to understand liquid-glass transition. Although the crystallization behaviors of various single-element liquids have been studied broadly in both experiments and simulations, the structural origin at atomic level of distinct glass forming abilities between fcc and bcc pure metals still remains a mystery. Here we report the distinct spatial gradient of atomic packing during the crystallization processes of two representative liquids: bcc zirconium and fcc copper. The different crystallization rates can be attributed to the distinct atomic packing features of the transition region between crystalline grains and supercooled liquid. The features of transition region is determined by the competition between locally favored structures of supercooled liquid and crystal-like bond orientational ordering, which reveals the crucial role of interface energy in determining the crystal growth rate, and thereby the glass forming ability.