Structure-Directing Agents of Chaordic Materials Using High-Entropy Alloying

For nearly a century, alloy design has been guided by the Hume-Rothery rules, which describe the conditions required for solid solution formation and have traditionally constrained the compositional space available to materials scientists. The emergence of high-entropy alloys fundamentally altered this paradigm by demonstrating that configurational entropy can stabilize compositions that would otherwise be thermodynamically unfavorable. Since their discovery, high-entropy concepts have expanded beyond metallic systems into ceramics, including oxides, carbides, silicides, nitrides, and borides, creating new opportunities to access unconventional chemistries and local atomic environments. This review examines how high-entropy alloying can be used to transcend classical alloying limitations and stabilize elements in coordination environments that are inaccessible in conventional materials. Particular emphasis is placed on high-entropy borides, where ordered boron frameworks provide a structural scaffold that accommodates chemically disparate elements while preserving phase stability. Recent examples, including Pt- and Si-containing high-entropy diborides, demonstrate how entropy stabilization enables the incorporation of elements that do not form stable binary diborides (MB2), resulting in unique electronic structures, bonding environments, and functional properties. More broadly, these systems illustrate how the interplay between disorder and local order can be leveraged to design next-generation materials beyond the boundaries imposed by traditional alloying rules.