Nanotwinned Boron Suboxide (B6O): New Ground State of B6O

摘要

Nanotwinned structures in superhard ceramics rhombohedral boron suboxide (R-B6O) have been examined using a combination of transmission electron microscopy (TEM) and quantum mechanics (QM). QM predicts negative relative energies to R-B6O for various twinned R-B6O (denoted as tau-B6O, 2 tau-B6O, and 4 tau-B6O), consistent with the recently predicted B6O structure with Cmcm space group (tau-B6O) which has an energy 1.1 meV/B6O lower than R-B6O. We report here TEM observations of this tau-B6O structure, confirming the QM predictions. QM studies under pure shear deformation and indentation conditions are used to determine the deformation mechanisms of the new tau-B6O phase which are compared to R-B6O and 2 tau-B6O. The lowest stress slip system of tau-B6O is (010)/< 001 > which transforms tau-B6O to R-B6O under pure shear deformation. However, under indentation conditions, the lowest stress slip system changes to (001)/< 110 >, leading to icosahedra disintegration and hence amorphous band formation.