Direct Observation of Solid-State Diffusion Using the Mössbauer Effect

Iron diffusion in copper has been measured using the Mössbauer effect. The temperature dependence of the Mössbauer line broadening is proportional to the temperature dependence of the diffusivity as determined by the tracer-sectioning technique. The magnitude of the broadening is about $\frac{\hslash }{\tau }$ (where $\tau$ is the mean time an atom spends at a given site), instead of $\frac{2\hslash }{\tau }$ as predicted by the jump model of diffusion. No evidence for sidebands is observed in the broadened Mössbauer spectra, which have approximately Lorentzian line shape. The temperature dependence of the recoil-free fraction appears to be anomalously large in the region where diffusion broadening of the Mössbauer line was observed.