First-principles insight of hydrogen dissolution and diffusion properties in ?-Al2O3

First-principles theory is applied to identify the structure of gamma-Al2O3 first. Then, hydrogen dissolution and diffusion behavior was further studied to reveal the reason that permeation reduction factor (PRF) of gamma-Al2O3 is lower than that of alpha-Al2O3. Our calculations show that the formation energy for Al vacancy at the octahedral interstitial site ( VAl-3 -OIS) is lower than that at the tetrahedral interstitial site ( V-3 Al -TIS), and are far lower than those of other defects in both defective spinel and non-spinel gamma-Al2O3. Thus, the stability of V-3 Al -OIS is higher than that of VAl-3 -TIS in both Al-rich and O-rich environments. However, when hydrogen atoms are introduced into gamma-Al2O3, the stability of [VAl-TIS-H] -2 is higher than that of [VAl-OIS-H] -2 in the defective spinel gamma-Al2O3 structure, while the opposite is true for the non-spinel gamma- Al2O3 structure. The vibrational frequencies for OH- in [VAl-TIS-H] -2 and [VAl-OIS-H] -2 for defective gamma- Al2O3 are calculated to be 3608 cm -1 and 3374 cm -1, respectively, which is in excellent agreement with the infrared (IR) absorption peaks observed at similar to 3500 and similar to 3300 cm -1. The defective spinel model is more suitable for describing the gamma-Al2O3 structure. In defective spinel gamma-Al2O3, there are many native Al vacancies, which are arranged in a straight line along the [ 2 1 over line 1 over line 0 ] direction. The migration barrier for H diffusion along these native Al vacancies is so low that these Al vacancies can provide a rapid diffusion channel for H. Thus, the permeability of H in gamma-Al2O3 is much higher than that in alpha-Al2O3 leading to a lower permeation reduction factor (PRF). Our results can provide not only a sound theoretical explanation for the low PRF of gamma-Al2O3 but also a direction to improve the efficiency in preventing H permeation through FeAl/Al2O3 tritium permeation barriers (TPBs).(c) 2022 Elsevier B.V. All rights reserved.