Atomic-scale structure of α-FeOOH containing chromium by anomalous X-ray scattering coupled with reverse Monte Carlo simulation

Quantitative X-ray structural analysis by applying anomalous X-ray scattering (AXS) has been used for characterizing the effect of chromium on the atomic-scale structure of α-FeOOH particles, which is a typical ferric oxyhydroxide in rust formed on the steel surface. The X-ray diffraction profiles showed that the fundamental structure of α-FeOOH containing chromium is similar to that of α-FeOOH particles without chromium. The realistic atomic-scale structures in α-FeOOH with and without chromium were estimated by fitting both the ordinary and environmental interference functions with model calculation using the reverse Monte Carlo (RMC) simulation technique. The results indicated that distortion of the linkage of FeO6 octahedral structural units in α-FeOOH is induced by chromium addition, but chromium addition to α-FeOOH fundamentally is likely to be substituted for iron in α-FeOOH. The atomic-scale arrangements in α-FeOOH with and without chromium were visualized using FeO6 octahedral units. These middle range ordering structures were correlated with the microscopic morphological change of particles by chromium addition.