Abstract
The predominant hydrogen-containing species in Ti (rutile) are O (hydroxyl) ions, in which the oxygen occupies a regular oxygen ion site, and the O-H bond is perpendicular to the axis. It is proposed that diffusion of hydrogen parallel to the axis proceeds by a proton jump from one ion to another along the channel as represented by O··· → ······ → ···H. It is also proposed that diffusion perpendicular to the axis proceeds by a rotation of the O bond to move the proton from one channel to an adjacent channel, followed by a proton jump to another ion in the same channel. From a potential-energy model, which includes a Morse function to represent the O bond, as well as electrostatic and repulsive terms, the activation energies for hydrogen and tritium diffusion parallel to the axis were calculated to be (including a zero-point energy correction) 0.60 and 0.69 eV, respectively, in good agreement with the respective experimental values of 0.59 and 0.75 eV. The calculated activation energy for diffusion perpendicular to the axis was 1.23 eV (no zero-point energy correction), as compared to the experimental values of 1.28 and 1.11 eV, respectively, for hydrogen and tritium. The calculated equilibrium orientation of the O ion in Ti and the calculated stretching frequency of this species were also in good agreement with the respective experimental results.
- Received 22 September 1978
DOI:https://doi.org/10.1103/PhysRevB.19.4130
©1979 American Physical Society