Order and Disorder in Amorphous and High-Entropy Materials

Order and disorder are important principles in materials science in which entropy is a measure of disorder in a system. For example, recently developed high-entropy alloys and amorphous alloys have drawn interest based on the ability to design their disorder to bring out different material characteristics. High-entropy alloys are controlled by chemical disorder, whereas amorphous alloys are governed by topological disorder. There is often a need to increase disorder or entropy in these materials to satisfy certain complex performance requirements. Here, we examine the roles of order, disorder, and entropy in amorphous and high-entropy alloys. Several key research topics are summarized, including high-entropy films, high-entropy ceramics, and high-entropy alloys. Moreover, there remain questions about the role of entropy stabilization in high-entropy ceramics. Here, we also report three novel porous light-weight high-entropy nitrides based on the NbTiAlSi system. Our findings clarify the general role of entropy in high-entropy ceramics.