Fast hydrogen diffusion along Σ13 grain boundary of α-Al2O3 and its suppression by the dopant Cr: A first-principles study

To acquire knowledge of the effect of chromium dopant bringing on hydrogen diffusion along grain boundaries (GBs) of alpha-Al2O3, the energetics and mobility of hydrogen along Sigma 13 GB with and without Cr dopant have been studied via the first-principles calculations with the projector-augmented wave method. The energy barriers for hydrogen diffusion before and after Cr doped on Al-terminated Sigma 13 GB are determined to be 0.69 eV and 1.09 eV, respectively, which is smaller than or close to the hydrogen bulk diffusion with an activation energy of 1.10 eV. The results suggest that before doping Cr atoms, there is a rapid and easy diffusion channel for hydrogen along the Sigma 13 GB. However, the calculations show the segregation of Cr atoms to the GB is energetic favorable with a segregation energy of -0.39 eV/atom, and the existence of Cr can suppress hydrogen diffusion along the Al-terminated Sigma 13 GB. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.