The large anisotropy of the diffusion coefficient for a substitutional randomly diluted cationic impurity in the rutile structure, with the diffusivity being much larger along the tetragonal axis as compared to the diffusivity within a tetragonal plane, indicates that open and almost empty 〈001〉 channels are involved along with an interstitialcy mechanism to originate diffusion events leading an impurity from one to another substitutional cationic site. This model is used to evaluate the resulting emission Mössbauer spectra of the impurity staying locally at equilibrium with the lattice and embedded in a single-crystalline sample. Final results are shown for the 14.4 keV Mössbauer line in ${}_{}{}^{57}{}_{}{}^{}\mathrm{Co}$ (Fe). It is shown that channel diffusivity is governed by the exponential law, and details of the electric-field-gradient relaxation due to the diffusive motion of the probe are described from first principles. © 1996 The American Physical Society.

• Received 11 March 1996

DOI:https://doi.org/10.1103/PhysRevB.54.4006