Tensile strength and fracture of a tilt grain boundary in cubic SiC: a first-principles study

The ab initio tensile test has been applied to the non-polar interface of t he {122}, Sigma = 9 tilt boundary in cubic SiC, where the tensile strength and mechanical behaviour at zero temperature are examined using the ab init io pseudopotential method based on the local density-functional theory. Thi s interface is strong because of the reconstruction of interfacial bonds. T he maximum tensile stress in the unaxial extension normal to the interface is about 42 GPa, which is about 80% of the theoretical and experimental val ues of the strength of bulk crystal along the [111] direction. Young's modu lus and the fracture toughness are also comparable with the values of the b ulk crystal. The back Si-C bond of the interfacial C-C bond is broken first because the C-C bond has a high strength and a short length like a diamond bond. Then the interfacial Si-C bonds are broken, and finally the Si-Si bo nd. The Si-C bonds are rapidly stretched and broken if the bond stretching exceeds about 20%, and the bond charge clearly disappears when the bond str etching exceeds about 30%. Changes in the electronic structure associated w ith the bond breaking are analysed.