First-Principles Calculations of Hydrogen Solution and Diffusion in 3C-SiC Grain Boundaries

First-principles calculations were employed to study the solution and diffusion properties of hydrogen (H) at the Si-rich and C-rich Σ3(111)[11¯0] (Σ3Si and Σ3C) and Σ9(221)[11¯0] (Σ9) grain boundaries (GBs) in 3C-SiC. We constructed GBs of varying sizes and calculated their formation energies and excess volumes to identify the stability of GBs. The Σ9 GB is more stable and has a relatively open structure compared with the Σ3 GB. The solution energies of H at the Σ3Si, Σ3C and Σ9 GBs are significantly reduced to 1.46, 2.30 and 1.47 eV, respectively. These values are much lower than that in the bulk. The negative segregation energies indicate that H is more likely to reside at the GBs rather than in the bulk. The diffusion energy barrier of H in the Σ3C GB is as high as 1.27 eV, whereas in the Σ3Si GB and Σ9 GB, the barriers are as low as 0.42 eV and 0.28 eV, respectively. These results suggest that H migration will be suppressed in the Σ3C GB but promoted in the Σ3Si and Σ9 GBs. The differences in H diffusion behavior among these three GBs may be attributed to the relatively more open structures of the Σ3Si and Σ9 GBs compared with the Σ3C GB. These results are essential for understanding the diffusion mechanism of H and its retention behavior in SiC.