Properties of iron impurities in beryllium from Mössbauer studies

Beryllium specimens containing 0.012-at.% ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ were studied by Mössbauer spectroscopy in the temperature range from 75 to 1200 K. The changes of the recoil-free fraction, the second-order Döppler shift, the isomer shift, the quadrupole splitting, and the peak intensities are reported and interpreted as follows. (i) The effective impurity-host force constant ${\lambda }^{\prime }$ is slightly smaller than the host-host force constant $\lambda (\frac{{\lambda }^{\prime }}{\lambda }\sim 0.96)$ and an anharmonic behavior is observed at high temperature. (ii) The main part of the electric field gradient arises from $d$ electrons localized around the impurity atom in a virtual bound state near the Fermi level. (iii) At about 870 K, a short-range diffusion process occurs for iron impurities in as-quenched specimens with progressive annealing of quenched defects.