It was noted that the diffusion coefficient of a randomly distributed substitutional cationic impurity in the rutile structure was markedly anisotropic; with the diffusivity being much greater along the tetragonal axis as compared with the diffusivity within a tetragonal plane. This indicated that open, and almost empty, <001> channels were involved; together with an interstitialcy mechanism which gave rise to diffusion events that led an impurity from one substitutional cationic site to another. This model was used to evaluate the resultant emission Mössbauer spectra of an impurity which remained in local equilibrium with the lattice and was embedded in a monocrystalline sample. Results were presented for the 14.4keV Mössbauer line in 57Co (Fe). It was shown that the channel diffusivity was governed by an exponential law.

Calculation of the Recoilless γ-Ray Emission Spectra from a Substitutional Cation Impurity Diffusing via the <001> Channels in the Rutile Structure. Ruebenbauer, K., Wdowik, U.D., Kwater, M.: Physical Review B, 1996, 54[6], 4006-20