Effects of Carbon Doping on the Structural, Energetic, and Electronic Properties of Intrinsic Defects in α-Al ₂ O ₃

The atomic-scale mechanisms governing the carbon doping effects in α-Al₂O₃ remain incompletely understood. Using density functional theory (DFT), we systematically investigate how carbon substitution modulates the structural, energetic, and electronic properties of α-Al₂O₃ with intrinsic defects. The findings reveal that structural distortion is strongly site-dependent. C substitution at oxygen sites (C_O) induces significantly greater lattice deformation than aluminum-site substitution (C_Al). Average distances from defect positions to neighboring atom analyses show that C doping preferentially perturbs the O atom distances in V_Al/Al_i systems, while dominantly affecting Al-atom distances in V_O/O_i systems. Furthermore, formation energies of intrinsic defects decrease by up to 35% with C doping under both O-rich and O-poor conditions. C_O doping most effectively stabilizes vacancies/interstitials, while C_Al preferentially lowers Frenkel pair energies. Aluminum vacancies (V_Al) exhibit the lowest formation energy. Additionally, C doping introduces midgap states through C 2p and O 2p hybridization, narrowing band gaps from 6.16 eV (pristine) to 1.60-4.45 eV. This work provides crucial insights into how carbon doping modulates defect formation and local structure in α-Al₂O₃, offering valuable guidance for the strategic design of alumina-based materials with tailored properties through fine-tuning defect engineering.