On the amorphous to crystalline structure transition of oxidized LEAs

Abstract

Oxide crystallization in multicomponent alloys is often delayed relative to mono-metals, yet the mechanisms underlying this behavior remain incompletely understood. Here, we investigate the relationship between oxygen saturation and crystallization in thin-film mono-metals and low-entropy alloys (LEAs) by introducing two temperatures in our annealing experiment: the thickness saturation temperature (Tf), marking completion of oxygen uptake, and the oxide crystallization temperature (T2), marking the onset of crystalline oxide formation. We show that mono-metals typically crystallize prior to or concurrent with saturation (T2 ≤ Tf), whereas LEAs generally show the opposite (T2 > Tf), indicative of delayed oxide crystallization. Therefore, we define the difference (T2 − Tf) as the crystallization delay strength (CDS), providing a quantitative metric for comparing oxide crystallization behavior across compositions. By correlating key oxide uptake saturation and crystallization temperatures (Tf, T2, thus also CDS) with bond-character descriptors derived from the Van Arkel–Ketelaar model, we show that bond ionicity and covalency systematically influence oxygen saturation and crystallization delay. We report that LEAs with higher ionicity show lower saturation temperatures Tf and increased crystallization delay, while more covalent alloys crystallize without significant CDS. These results establish bond character as a predictive descriptor for oxide crystallization behavior in alloy thin films.