Interaction of C with vacancy in W: A first-principles study

We provide a vacancy trapping mechanism of C in W by investigating structure, stability, and diffusion properties of C in W using a first-principles method. C easily bonds onto the internal-surface of vacancy. A monovacancy is capable of trapping as many as 4 C atoms to form CnV (n = 1, 2, 3, 4) complexes. Single C atom prefers to interact with neighboring W at vacancy with the trapping energy of −1.93 eV. With the C atoms added, both of them are preferred to bind with each other to form covalent-like bond despite the metallic W environment. For the CnV complexes, C2V is the major one due to its largest average trapping energy (−1.97 eV). Kinetically, formation of the CnV complexes can be ascribed to the interstitial mechanism due to the lower activation energy barrier of 1.46 eV for the interstitial C than 1.66 eV for the vacancy.

► Tungsten (W) and W alloys are considered as the most promising plasma facing material.
► Impurity carbon has large effect on the properties of W.
► Defect vacancy can easily trap carbon atoms to form CnV complexes.