Shear band formation during nanoindentation of EuB6 rare-earth hexaboride

Research on rare-earth hexaborides mainly focuses on tuning their electronic structure from insulating-to-metallic states during high pressure experiments. However, the structural evolution that contributes to their mechanical failure is not well understood. Here, we examine the pressure-induced structural evolution of a model rare-earth hexaboride, EuB 6 , during nanoindentation. Transmission electron microscopy reveals that nanoscale amorphous shear bands, mediated by dislocations, play a decisive role in deformation failure. Density functional theory calculations confirm that amorphous bands evolve by breaking boron-boron bonds within B 6 octahedra during shear deformation. Our results underscore an important damage mechanism in hard and fragile hexaborides at high shear pressures. Rare-earth hexaborides are of interest for their pressure-induced phase transformations, but further understanding is needed regarding their failure mechanisms. Here, nanoindentation of EuB 6 causes dislocation-mediated shear band formation, driven by the breaking of boron-boron bonds.