A model was developed which described the diffusivity of a highly dilute and randomly distributed substitutional cationic impurity via open, and almost empty, <001> channels in the rutile structure. The model was based upon the assumption that an insignificant fraction of the impurities resided in the channels. The model was extended, so as to allow for a significant fraction of resident impurity in the channels, and was used to evaluate emission Mössbauer spectra which originated from diffusing impurities in monocrystalline samples. Results were presented for the 14.4keV Mössbauer line of 57Co. It was shown that the spectral line positions depended upon wave-vector transfer to the system, and that the data were sensitive to the fractions of both parent and daughter impurities which resided in the channels.

K.Ruebenbauer, U.D.Wdowik, M.Kwater, J.T.Kowalik: Physical Review B, 1996, 54[18], 12880-91