PNNL

Abstract

The analysis of defects generated by displacement cascades in silicon carbide shows that most defects are point defects that are displaced at a small distance from their original sites. These defects play important roles in the recovery processes observed experimentally. Only 20% of total the interstitials produced become freely migrating defects that can contribute to microstructural evolution during irradiation of SiC. The stable defect configurations in this study were created with low-energy recoils using molecular dynamics (MD) methodology, with most defects being C Frenkel pairs. These stable Frenkel pairs have been annealed at different temperatures, using MD methods, to determine the time required for interstitials to recombine with vacancies. The MD data have been analyzed using an Arrhenius relation, and the estimated activation energies for defect recovery is between 0.22 and 1.6 eV for C Frenkel pairs and between 0.28 and 0.9 eV for Si Frenkel pairs. The low activation energies qualitatively overlap with experimental values observed during Stage I recovery. Thus, the present results suggest that the Stage I is associated with the spontaneous recovery of Frenkel pairs. Based on the data obtained, the spontaneous recombination distance is determined to be 0.66 and 0.70 ao for the C and Si sublattices, respectively.