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Tetragonal boron (T-B 50) in elementary boron phases is suggested to be mechanically unstable due to the electron deficiency in icosahedral framework. Here we identified a unique distorted structure in T-B 50 that stabilizes this phase by combining high-resolution transmission electron microscopy (HRTEM) and quantum mechanics (QM) simulations. Experimentally by using HRTEM in T-B 50 crystal along 〈 101 〉 orientation, we show that large shear strain and lattice rotation at the proximity of planar faults stabilize the structure. QM simulations ascertained that the vacancy and shear deformation play an important role in the formation of the distorted structure observed experimentally. More interesting, QM simulations show that the distorted structure is similar in energy to the perfect tetragonal structure, but lower in energy than the vacancy structure. The origin of stabilization of distorted structure arises from satisfying the electron counting rule for B 12 icosahedral clusters. Image, graphical abstract [ABSTRACT FROM AUTHOR]

We report the formation of shear-induced amorphization in elemental β‑boron (β-B) using transmission electron microscopy (TEM) and density function theory (DFT) simulations. TEM observations beneath the residual indentation of β-B revealed intragranular nanoscale shear bands along 1 ¯ 1 1 ¯ and 111 crystallographic planes, which are preceded by nucleation of dislocations. Strain map analyses of the shear band indicated that compressive strain assists in the process of bond breaking and shear strain is involved in the disassembly of icosahedral clusters by forming amorphization within a unit cell of β-B. Further DFT simulations confirmed that the deconstruction of triply fused icosahedral (B 28) along 1 1 ¯ 0 111 slip system in β-B 106 has the lowest shear strength leading to the formation of a kink followed by amorphization, which is in line with our experimental observations. This study illustrates the structural evolution of shear amorphization in β-B and provides the basis to improve their mechanical properties through modification of internal structure. [Display omitted] • Accurate structural evolution of amorphization in elemental β-B are observed using HRTEM. • Nanoscale amorphous bands proceed by nucleation of dislocations. • Compressive- and shear strain assist the disassembly of intra-icosahedra clusters within the amorphous band of β-B. • The deconstruction of triply fused icosahedral (B 28) in β-B 106 leading to a kink and amorphization confirmed by DFT. [ABSTRACT FROM AUTHOR]