Influence of substitutional impurities on hydrogen diffusion in B2-TiFe alloy

The hydrogen diffusion pathways were studied in B2-TiFe alloy within density functional theory (DFT) using the plane-wave pseudo-potential method. Our results confirm that the hydrogen diffusion between octahedral interstices where it is surrounded by two Fe and four Ti atoms along [10-1] direction is most preferential in TiFe bulk. The estimated hydrogen diffusion barrier of 0.62 eV differs insignificantly from values of barriers in pure Ti. The influence of substitutional transition and simple metal impurities on the energy barriers is discussed. It was found that impurities such as V, Cr, Mn decrease the hydrogen diffusion barriers along both considered pathways whereas Pd impurity decreases considerably the barrier along [00-1] direction that leads to the change of the diffusion mechanism. In general, the competition of structural and electronic factors strongly influences the hydrogen diffusion barriers. The present results provide a deep understanding of H behavior in TiFe bulk.