Determination of manganese oxidation states in solids by electron energy-loss spectroscopy

Electron energy-loss spectra of manganese-bearing phases vary systematically with changes in the average oxidation state of manganese. The energy region recorded, 0 to 1000 eV, includes electronic transitions from manganese and oxygen core orbitals, as well as from states that have contributions from both elements. We used a spectrometer attached to a transmission electron microscope (TEM) to obtain reference spectra from manganese metal and from manganese oxides that contain Mn2+, Mn3+, and Mn4+. Such reference spectra can be used to estimate the manganese oxidation state for uncharacterized manganese-bearing solids. Areas with diameters as small as 0.1 μm can be analyzed, thus avoiding the uncertainties associated with bulk analyses of fine-grained, heterogeneous mixtures. Similar determinations of reference energy-loss spectra for other polyvalent elements will broaden the applicability of this technique for the study of small volumes of solids.