Sensitivity of SiC Grain Boundaries to Oxidation

Molecular dynamics simulations of dry oxidation of bicrystals with incoherent and coherent grain boundaries (GBs) in 3C-SiC are performed at 2000 K and the results are compared to oxidation of single-crystal SiC. Oxidation near incoherent GBs is found faster than that in single crystals and in coherent GBs, whereas oxidation of coherent GBs is comparable to that of single crystals. The accelerated oxidation near incoherent GBs is attributed to strain and the presence of under-coordinated Si within the GB region, both of which reduce the positive charge on silicon atoms, making them more reactive with oxygen. Although atoms with similar properties are found in dislocation cores of coherent GBs, dislocation cores are isolated from each other by crystalline regions, which in turn control the rate of oxidation.