A comparative ab initio study of the ‘ideal’ strength of single crystal α- and β-Si3N4

Abstract In this study, the ideal tensile and shear strengths of single crystal α- and β-Si3N4 were calculated using an ab initio density functional technique. The stress–strain curve of the silicon nitride polymorph was calculated from simulations of predefined strain deformation in various directions. In particular, the ideal strength calculated for an applied tensile γ11 strain, in the [1 0 0] plane, was estimated to be ∼51 and 57 GPa, for α- and β-Si3N4, respectively. Using a reported empirical method an estimate was also made of the Vickers indentation hardness of the α- and β-Si3N4 single crystals, ∼23.0 and 20.4 GPa, respectively. Moreover, a hardness estimate has been reported for Si3N4 in the literature: ∼21.0 GPa.