First principles calculations of hydrogen-induced decrease in the cohesive strength of α-Al2O3 single crystals

First principles calculations were conducted to investigate the effects of hydrogen on the cohesive strength of α-Al2O3 single crystals. The results show that the cohesive strength of α-Al2O3 single crystals decreases with increasing hydrogen concentration, CH. For example, the cohesive strength along the [0 0 1] direction, σth(0 0 1), decreases from 48.9 GPa (CH = 0) to 46.2 GPa (CH = 1630 wppm) and 39.6 GPa (CH = 4900 wppm). The lattice expansion and the changes in the local electronic structure caused by the hydrogen atoms are the two main reasons for the decrease in the cohesive strength. The results provide a computational evidence for the hydrogen-induced decrease in cohesive strength, which can explain the experimental phenomenon of hydrogen-assisted delayed fracture in α-Al2O3 ceramics during charging of hydrogen under a sustained load.