Multiscale cascade triggered by the vacancy-[Si + C] synergy in β-SiC: a first-principles study of...

The degradation of β-SiC under irradiation manifesting as swelling and amorphization originates from the accumulation and interaction of atomic-scale defects. While single vacancies have been studied, the synergistic role of vacancy complexes, particularly the divacancy, as potential seeds for cascade damage, remains poorly understood. Here, we employ ab initio molecular dynamics (AIMD) to systematically investigate the vacancy-[Si + C] in β-SiC to reveal its function as a cooperative defect unit that triggers multiscale instability. Unlike a linear superposition of individual vacancy effects, the vacancy-[Si + C] induces nonlinear synergy and initiates with electron cloud delocalization evidenced by fragmented electron localization function. This electronic perturbation cascades into severe short-range lattice disorder, suppressed mid-range atomic mobility and global phonon mode softening. We elucidate a coherent electron-structure-dynamics coupling mechanism. Vacancy-[Si + C] as a synergistic defect core whose coupled lattice strain and electron delocalization effect destroy the periodic bonding of β-SiC, causing large-scale lattice disorder. This work establishes a novel defect-origin perspective for irradiation damage in β-SiC, revealing the vacancy-[Si + C] as a prototypical synergistic defect seed that triggers a multiscale damage cascade. The coupled electron-structure-dynamics approach developed here offers a generalizable paradigm for deciphering complex defect behaviors in covalent materials, providing critical guidance for vacancy-engineering strategies in β-SiC based functional materials.