Influence of radiation-damage evolution on lattice-location measurements for Yb and Au in iron

The influence of radiation damage on the lattice location of heavy impurities (Yb and Au) implanted in iron is studied by channeling experiments. The nature of the impurity-radiation-damage interaction has been modified by annealing of room-temperature implanted samples or high-temperature implantation. The value of the corrected extinction ratio $\epsilon$ measured in several crystallographic directions on room-temperature implanted Yb and Au impurities cannot be interpreted uniquely in terms of different site populations. The annealing- and implantation-temperature dependences of the ratio $\epsilon$ for Yb-implanted Fe are very different. Upon annealing, the value of $\epsilon$ is unchanged up to 450°C and then drops abruptly. In hot-implant experiments, the extinction ratio starts to fall at ∼150°C when vacancies become mobile. Vacancy-assisted diffusion is suggested to cause the changes of $\epsilon$ in both experiments. The temperature dependence of $\epsilon$ for the (100) plane is found to differ from that in other directions. This planar effect suggests that Yb impurities move preferentially in the (100) plane, which is the plane of vacancy loops in Fe. A quantitative analysis of these lattice-location results and of related hyperfine-interaction results is presented in a companion paper.