Measurements of H and D diffusion were performed by using an isotope exchange technique. Use of this technique resulted in measurements which were accurately described by Fick’s law with a constant diffusion coefficient, as predicted theoretically. This was in sharp contrast to single ion diffusion, where marked departures from classical diffusion theory were observed. The measured diffusion coefficients for H were described by:

a-axis:     D(cm2/s) = 3.8 x 10-1exp[-1.28(eV)/kT]

c-axis:     D(cm2/s) = 1.8 x 10-3exp[-0.59(eV)/kT]

Ionic conductivity measurements were also reported which agreed well with the bulk diffusion measurements, and permitted extension of the range of measurements, for c-axis diffusion, from 125 to 750C; corresponding to a range of more than four orders of magnitude in D. The measured diffusion parameters were found to be essentially independent of sample purity, although it was observed that significant concentrations of lattice defects sharply inhibited H diffusion.

Diffusion of H and D in TiO2: Suppression of Internal Fields by Isotope Exchange. Johnson, O.W., Paek, S.H., DeFord, J.W.: Journal of Applied Physics, 1975, 46[3], 1026