Hydrogen diffusion in doped and undoped α-Ti: An ab-initio investigation

• H preferential path in α-Ti along [0001] direction is O1→T1→T2→O2.
• The lowest energy barrier of 0.1 eV was found between T-sites along c axis.
• Influence of impurities on the key barriers for H diffusion in α-Ti is discussed.
• Impurities of simple metals hamper H mobility increasing activation energy.
• 3d metals of middle of period provide the decrease of H barriers for OT, OO jumps.

The hydrogen diffusion paths in undoped and doped α-Ti were studied by the projector augmented wave method within the density functional theory. Our calculations confirm that in the basal plane, the indirect mechanism of hydrogen diffusion between octahedral sites through a tetrahedral interstitial is more preferable than the direct path. The lowest energy barrier of 0.1 eV was found between the tetrahedral sites along the c axis; however, a hydrogen atom can only oscillate between them. The influence of substitutional impurities (transition- and simple-metal ones) on the main barriers is discussed. It was found that impurities of simple metals hamper the H mobility by increasing the activation energy, whereas most transition-metal solutes (3d-metals of group 5–10) reduce the energy barriers. In general, a deeper understanding of the H diffusion behavior in doped α-Ti is achieved. The temperature-dependent diffusion coefficient and the activation energy for hydrogen atom hopping along the preferential path in pure titanium are found to be in agreement with the experimental data.