Intrinsic dense twinning via release of native strain

Icosahedral boron-rich solids exhibit outstanding mechanical properties, but the crystal structure of this prominent class of materials has long remained enigmatic. Here, we report on a surprising discovery of an unprecedented twinning induced structural stabilization that creates highly nanotwinned crystal structures that are stabler than the prevailing single crystal structure comprising complex multi-atom structural units. This phenomenon is showcased via a symmetry guided optimization process that produces a series of increasingly nanotwinned B4C structures with progressively lower energy below that of the single crystal, and this behavior also occurs in multiple other boron-rich solids. These findings unveil a distinct paradigm of defect (twinning) induced structural stabilizing mechanism that reduces energy via release of native strains built in the complex structural units of the single crystal, creating an exceptional category of materials that comprise multiple domains of intrinsic dense twinning in the crystal structures.