Ab initio study of the tensile strength and fracture of coincidence tilt boundaries in cubic SiC: Polar interfaces of the {122} Σ=9 boundary

Masanori Kohyama
Phys. Rev. B 65, 184107 – Published 3 May 2002
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Abstract

The tensile strength and fracture of polar interfaces of the {122} Σ=9 coincidence tilt grain boundary in cubic SiC have been examined through the behavior of electrons and ions using the ab initio pseudopotential method based on the local density-functional theory. The results are compared with previous results for the nonpolar interface of this boundary [M. Kohyama, Philos. Mag. Lett. 79, 659 (1999)], and the effects of interfacial configurations associated with Si-Si or C-C wrong bonds on the mechanical properties are discussed. In stable configurations of the N-type and P-type polar interfaces, all the interfacial bonds are well reconstructed similarly to the nonpolar interface, and the N-type and P-type interfaces contain C-C and Si-Si wrong bonds, respectively, although the nonpolar interface contains both kinds of wrong bonds. An ab initio tensile test has been applied to the supercell containing both types of polar interfaces, where uniaxial tensile strain normal to the interface is applied in small increments. Only the P-type interface is broken just after the maximum tensile stress of about 48 GPa and the N-type interface is not broken at all. This tensile strength of the P-type interface is larger than that of the nonpolar interface of about 42 GPa, and the N-type interface containing C-C bonds is the strongest. The tensile strength of all the reconstructed interfaces is rather large, and is over 80% of the theoretical and experimental strength of bulk SiC. A critical bond stretching of about 20% is observed for the Si-C bond breaking, similarly to the case of the nonpolar interface. It is shown that the atomic-scale inhomogeneity or singularity associated with the wrong bonds seriously affects the tensile strength and interfacial fracture. For the nonpolar interface, the fracture starts from the back Si-C bond of the C-C bond because of local stress concentration at the atomic scale, and proceeds from bond to bond rather continuously. For the P-type polar interface, on the other hand, there occurs no remarkable local stress concentration except for just before the fracture, because of the highly symmetric configuration. Thus larger tensile strain and stress are introduced before the fracture, and a larger number of interfacial bonds reach the criterion of bond breaking at the same time. This is the reason why the P-type polar interface containing Si-Si bonds is stronger than the nonpolar interface and is broken rather catastrophically. The present results should be applicable to general coincidence tilt grain boundaries in SiC with similar reconstructed configurations.

  • Received 6 September 2001

DOI:https://doi.org/10.1103/PhysRevB.65.184107

©2002 American Physical Society

Authors & Affiliations

Masanori Kohyama

  • Interface Science Research Group, Special Division of Green Life Technology, National Institute of Advanced Industrial Science and Technology, 1-8-31, Midorigaoka, Ikeda, Osaka 563-8577, Japan

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Issue

Vol. 65, Iss. 18 — 1 May 2002

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