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

The hydrogen diffusion paths in undoped and doped alpha-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 alpha-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. (c) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.