The arrangement of interstices in the hcp lattice (left panel) and the energy profiles for a hydrogen atom to diffuse along (a) , (b) , and (c) and paths.
Calculated phonon dispersions of a 36-atom α-Ti supercell with hydrogen, deuterium, and tritium atoms in the stable octahedral site (Oct), the transition states along the (TS-OO), (TS-OT), and (TS-TT) paths, and the metastable tetrahedral site(Tet), respectively. The modes with imaginary frequencies at the transition states correspond to the motion of the hydrogen, deuterium, and tritium atoms across the barriers.
Calculated and experimental diffusion coefficients of atomic hydrogen, deuterium, and tritium in α-Ti. The T tr = 1155 K stands for the phase transition temperature of metal Ti from α-phase to -phase.
The ratios of the diffusivity of deuterium and tritium to hydrogen atoms. ( ) and ( ) represent the impurity diffusions perpendicular to and parallel to c axis, respectively.
Calculated migration enthalpy difference of atomic hydrogen diffusion via path, path, path, and path for 3 × 3 × 2 and 4 × 4 × 3 hcp Ti supercell models, respectively.
Calculated diffusion pre-factors ( and ) and activation energy ( and ) for atomic hydrogen, deuterium, and tritium in α-Ti. The temperatures represent the ranges over which diffusion coefficients were fit to extract corresponding pre-factors and activation energies. For comparison, experimental results are also listed.
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