Extended model of the channel diffusivity in the rutile structure

A model describing the diffusivity of a highly diluted and randomly distributed substitutional cationic impurity via the open and almost empty 〈001〉 channels in the rutile structure has been developed recently. The above model is based upon the assumption that the insignificant fraction of the impurities resides in the channels. An extended model is developed that allows for a significant fraction of the impurities to stay within channels, and it is used to evaluate emission Mössbauer spectra originating from the diffusing impurities embedded in single-crystalline samples. Final results are shown for the 14.4-keV Mössbauer line in ${}_{}{}^{57}{}_{}{}^{}\mathrm{Co}$(Fe). It is shown that spectral line positions depend upon the wave-vector transfer to the system, and that the data are sensitive to the fraction of both parent and daughter impurities residing in the channels. © 1996 The American Physical Society.