Ab initio study of the stability of intrinsic and extrinsic Ag point defects in 3CSiC

We have systematically investigated the energetics and stability of Ag atom in 3CSiC with various charge states using first-principles calculations within large supercells. Up to 18 Ag-defect configurations have been examined, including substitutionals, interstitials, and vacancy-based complexes. A general trend is that the formation energy of Ag-defect complexes is generally lower than interstitial typed defects. With the lowest formation energy, the configuration with Ag_TSi-V_C³⁺ turns out to be the most stable one. It has also been found a neutral Ag is more likely to substitute a silicon lattice site with a nearest carbon vacancy, thus forming an Ag_Si-V_C pair. All these data are important inputs in the next coarser-level modeling to understand the Ag migration in and release from 3CSiC under both thermal and radiation conditions.