Strong Trapping Capability and Diffusion Suppression Effect of Silicon Carbide Surface on Tritium: A First Principle Study.

Silicon carbide (SiC) has attracted considerable interest for use in electronics, aerospace, and nuclear energy applications owing to its excellent electrical and mechanical properties. In the nuclear industry, SiC serves as an effective tritium permeation barrier. However, a significant discrepancy remains between the experimentally measured diffusion coefficients and the theoretical predictions. In addition, a steep tritium concentration gradient exists near the surface, whereas the concentration remains nearly uniform through the bulk, a phenomenon that is not yet fully understood. In this study, first-principles calculations were performed to investigate the influences of vacancies, grain boundaries, and surfaces on tritium diffusion in 3C-SiC. Vacancies and grain boundaries were found to have a negligible impact on the effective diffusion coefficient. In contrast, the surface exhibited a high diffusion barrier, demonstrating a strong tritium-trapping behavior. Incorporation of the surface effect into a multilayer diffusion model resulted in good agreement between the theoretical predictions and the experimental results, while also explaining the observed steep concentration gradient near the surface. These findings enhance the fundamental understanding of the tritium behavior in SiC and provide theoretical guidance for the design of high-performance tritium permeation barrier materials.