Mössbauer study of localized diffusion in an interstitial cage

Abstract

Mössbauer investigations at various temperatures and in different directions with respect to an electron irradiatedAl ⁵⁷Co/⁵⁷Fe single crystal are reported. It is shown that the drastic decrease of the measured Mössbauer intensity in a narrow temperature range above 15 K is due to localized diffusion of Fe in an interstitial cage. The existence of the diffusive motion is demonstrated by the observation of a broadened component in the Mössbauer spectra above 15K. From the temperature dependence of the broadening the activation energy of the cage jumps is determined as 18±1 meV. Mössbauer spectra measured at sufficiently high temperature show only an unbroadened component, its intensity depending on the crystal orientation relative to the spectrometer. Comparison of this anisotropy with model calculations of the preceding part I of this paper shows that the Fe atom jumps between the corners of a cube, these corners being 0.52±0.02 Å distant in 〈111〉 directions from the octahedral lattice position.