Point defects production and energy thresholds for displacements in crystalline and amorphous SiC

Abstract

Molecular dynamics (MD) simulations are performed using the Tersoff + ZBL potential to determine the values and directional dependence of the threshold displacement energies (TDEs) for the production of point defects by carbon and silicon primary knock-on atoms (PKAs) with energies up to 400 eV in 3C-SiC and amorphous SiC (a-SiC). These materials are being considered for accident tolerant cladding materials in next generation light-water nuclear reactors and are being used in many other industrial applications. Results show that the TDEs for the displacement of a PKA or an atom in 3C-SiC, as well as those for the production of a Frenkel pair are different and highly anisotropic. The lowest energy to produce a carbon vacancy in any crystallographic direction is 14–16 eV and 38–58 eV for the C and Si PKAs, respectively. The lowest energies for the C and Si PKAs to produce a Si vacancy are 59–71 eV and 42–46 eV, respectively. The number of C vacancies produced by 400 eV C PKA and Si PKA are 4x and 1.75x the silicon vacancies produced, respectively. In a-SiC, the TDE probability distributions for the displacement of Si PKAs and of an atom differ, but are similar for C PKAs. The Si PKAs are likely to displace the less-massive C atoms at energies lower than that required to displace a Si PKA, resembling the interaction sequences in some directions in 3C-SiC. The energy to cause a C PKA displacement with 50% probability in 3C-SiC (26 eV), is more than twice that in a-SiC (13 eV). For the Si PKAs, these energies are 48 eV and 27 eV, respectively. The determined TDEs, which are consistent with the reported experimental values and those based on MD simulations, could be used in future investigations of irradiation effects.