The tensile strength and fracture of polar interfaces of the {122} Σ = 9 coincidence tilt grain boundary in cubic material were examined, via the behavior of electrons and ions, using an ab initio pseudopotential method which was based upon local density-functional theory. The results were compared with previous results for the non-polar interface of this boundary, and the effects of interfacial configurations associated with Si-Si or C-C wrong bonds on the mechanical properties were considered. In stable configurations of the N-type and P-type polar interfaces, all of the interfacial bonds were well-reconstructed (similarly to the non-polar interface) and the N-type and P-type interfaces contained C-C and Si-Si wrong bonds, respectively, although the non-polar interface contained both types of wrong bond. An ab initio tensile test was applied to a super-cell which contained both types of polar interface, where an uniaxial tensile strain normal to the interface was applied in small increments. Only the P-type interface was broken just after the maximum tensile stress of about 48GPa, and the N-type interface was not broken at all. The tensile strength of the P-type interface was higher than that (about 42GPa) of the non-polar interface, and the N-type interface which contained C-C bonds was the strongest. The tensile strengths of all of the reconstructed interfaces were quite high, and amounted to over 80% of the theoretical and experimental strengths of bulk SiC.

Ab initio Study of the Tensile Strength and Fracture of Coincidence Tilt Boundaries in Cubic SiC - Polar Interfaces of the {122} Σ = 9 Boundary. M.Kohyama: Physical Review B, 2002, 65[18], 184107 (11pp)