First principles study of the C/Si ratio effect on the ideal shear strength of β–SiC

The effect of the C/Si atomic ratio on the ideal shear strength of β-SiC is investigated with first principles calculations. $\beta -$SiC samples with different C/Si ratios are generated by Monte Carlo (MC) simulations with empirical inter-atomic SiC potential. Each SiC sample is sheared along the $⟨100⟩$ direction and the stress-strain curve is calculated from first principles. The results show that the ideal shear strength of SiC decreases with the increase of C/Si ratio. For a non-stoichiometric SiC sample, a C–C bond inside a large carbon cluster breaks first under shear strain condition due to the internal strain around the carbon clusters. Because the band gap is narrowed under shear strain conditions, a local maximum stress appears in the elastic region of the stress-strain curve for each SiC sample at certain strain condition. The yield strength may increase with the increase of C/Si ratio. (paper)