Electronic and Crystal-field Effects in the Fine Structure of Electron Energy-loss Spectra of Manganites

The fine structure of oxygen-K electron energy-loss spectra (EELS) of transition-metal oxides is known to correlate with nominal oxidation states (NOSs) that are often interpreted as charge states. Here we report calculations of O-K EELS in LaxCa1-xMnO3 that agree with measured spectra and show that the variation in the prepeak's intensity with doping is controlled by the orbital occupancy of the majority-spin Mn 3d states, while its width is controlled by crystal-field splitting. The results confirm an earlier conclusion that the NOS extracted from EELS corresponds only to orbital occupancies, while the physical charge renders all atoms electrically neutral, even in so-called ionic crystals.