Monatomic glass formation through competing order balance

The phase transformation of single-element systems is a fundamental natural process with broad implications, yet many aspects remain puzzling despite their simplicity. For instance, transition metals, Tantalum (Ta) and Zirconium (Zr), commonly form body-centred cubic crystals when supercooled. However, according to large-scale computer simulations, their crystallisation rates can differ by over 100 times. We reveal that this difference originates from stronger competing ordering effects in Ta than Zr. The key thermodynamic factor governing these kinetics is interfacial energy reduction through preordering in a supercooled liquid state. In Ta, strong competition between crystallisation and quasi-crystallisation occurs through non-classical pathways facilitated by crystal-like preordering and hierarchical icosahedral ordering. Conversely, Zr lacks this competing effect, leading to ultrafast crystallisation. These distinct features influence their glass-forming ability, potentially explaining the experimental synthesis of glassy Ta over other metals. Our findings provide insights into the formation mechanisms of glasses, crystals, and quasi-crystals of chemical elements.