Extraction of the local coordination and electronic structures of FeO_6 octahedra using crystal field multiplet calculations combined with STEM-EELS

摘要

The material properties of metal oxides are sensitive to even low levels of cation doping, and the local atomic structures around such trace elements in a crystal will differ from the bulk structure due to the different ionic size and electron configuration. The present work explores the extraction of the local structure of a minority component contained in an atomic column by analyzing the Fe L_(2,3) energy-loss near-edge structure of atomic-resolution monochromated electron energy-loss spectra, using crystal field multiplet calculations. The crystal field splitting of the Fe 3d state and the local coordination structure of FeO_6 octahedra in iron oxides in real space with known structures were determined. The results closely agreed with structures obtained from neutron diffraction and the Fe 3d DOS generated by density functional theory calculations. The previously unknown local structure of FeO_6 octahedra present at octahedral sites as a minor component (14.4%) in the brownmillerite structure of Ca_2Fe_(1.07)Mn_(0.93)O_5 was determined. This structure was found to be unique and differed from the results obtained using neutron diffraction, which reflect those of mainly MnO_6 octahedra. The present method is evidently an effective means of investigating the local structures around trace elements.