Density functional theoretical assessment of titanium metal for adsorption of hydrogen, deuterium and tritium isotopes

Abstract

Titanium, a high temperature tolerance metal is preferred as neutron targets due to high hydrogen storage capacity. Therefore, there is a need to understand the interaction and dynamical behaviours of hydrogen isotopes with Ti which is investigated by means of linear combination of atomic orbitals (LCAO) and projector augmented wave (PAW) potential within the density functional theoretical framework. The hydrogen isotope is studied by incorporating zero point energy and the harmonic transition state theory (HTST) were used to determine the rate constant. The values of surface adsorption energy of hydrogen isotopes were predicted to follow the trend: E ad (H 2 ) > E ad (D 2 ) > E ad (T 2 ). The activation energy barrier from top to bridge and top to hollow sites was negative for H atom indicating barrier less diffusion. The computed total density of states (TDOS) and partial density of states (PDOS) con rmed that the hollow site offers the most stable site for H atom adsorption than that by bridge and top sites. The calculated barrier height for dissociation was 0.4eV at surface coverage of θ H > 0.5ML whereas the barrier height for recombination was found to be much higher than that of dissociation. The calculated dissociation rate constant using HTST was found to be quite fast whereas the rate constant for recombination was determined to be very slow as expected. The ZPE corrected activation heights for bulk diffusion in Ti from one T d void to nearby Td void for H, D and T were computed to be 0.118, 0.126 and 0.129 eV respectively at the PAW level. The calculated diffusivity establishes that the lighter H atom migrates faster than that of heavier D and T atoms. The classical barrier height was observed to be reduced after quantum correction.