Plasticity of diamond compared to cubic BN

Owing to the same symmetry and very close lattice constants, diamond and cubic boron nitride (cBN) possess very similar physical properties, such as being superhard and brittle at ambient conditions. Here, the generalized stacking fault energy (GSFE) of different slip systems for diamond and cBN were calculated from first principles. The results show the perfect dislocation in diamond on the {100} plane dominates, while it is the {111} plane for cBN. This distinct difference originated from the saddle-shaped GSFE curve in diamond compared to the Gaussian line shape in cBN. Interestingly, the {111} slip plane of cBN remains unchanged under normal compression, while in diamond there is a transition from a {100} to {111} slip plane at a critical normal stress. This study provides an atomistic understanding of the experimental findings of room-temperature plasticity in diamond.