Multihyperuniform long-range order in medium-entropy alloys

Medium-entropy alloys (MEAs) and high-entropy alloys (HEAs) are alloys composed of mixtures of equal or relatively large proportions of three or more elements, and are distinctly different from traditional metallic alloys which contain one or two major components with smaller amounts of other elements. Recently MEAs and HEAs have received extensive research attention because they are found to possess superior mechanical performance, unusual thermal and electronic transport properties, and are resistant to corrosion; however, a fundamental understanding of the atomic structures of these alloys is still largely lacking. In this work, we develop a multihyperuniform (MH) model for disordered medium-entropy alloys (MEAs), in which the normalized infinite-wavelength composition fluctuations for all atomic species are completely suppressed, i.e., a model with hidden long-range order. Using SiGeSn alloy as a representative example, we show that this new type of highly efficient generic computational model results in stable lower-energy states compared to prevailing alloy models with (quasi)random structures, and captures experimentally observed atomic short-range orders in MEAs that are missing in (quasi)random alloy models. The MH model approximately realizes the Vegard's law, which offers a rule-of-mixture type predictions of the lattice constants and electronic band gap, and thus can be considered as an ideal mixing state. The multihyperuniformity also directly gives rise to enhanced electronic band gaps and superior thermal transport properties at low temperatures compared to (quasi)random structures, which open up novel potential applications in optoelectronics and thermoelectrics. Our MH model can be readily applied and generalized to other medium- and high-entropy alloys (HEAs) with atomic short-range orders, and may account for some of the previously observed major discrepancies between theory and experiment.