Oxidation states of Mn and Fe in various compound oxide systems.
Energy-loss near-edge structure (ELNES) data of Mn-L(2,3) and Fe-L(2,3) ionization edges have been measured by means of quantitative electron energy-loss spectroscopy (EELS) for two series of Mn and Fe oxides with known formal cation oxidation states. In both series the absolute energy positions of Mn-L(2,3) and Fe-L(2,3) white-lines, as well as the white-line intensity ratio (L3/L2) vary with cation oxidation states. Additionally, spin-orbit spitting, i.e. the energy difference deltaE(L2-L3) between Mn-L(2,3) white-lines decreases with increasing Mn oxidation state. With these data from known standards calibration curves on white-line intensity ratio Mn(L3/L2) vs. Mn oxidation state, and Fe(L3/L2) vs. Fe oxidation state were established. EELS measurements on Mn and Fe doped ZnO thin films showed that the valence states of the dopants can unambiguously be determined by calibrating the Mn-L(2,3) and Fe-L(2,3) ELNES data against the measured standards. It is revealed that Mn in ZnO adopt a divalent state, thus Mn2+ ions substitute for Zn2+, whereas Fe dopants retain a trivalent oxidation state in the ZnO host lattice. Measurements on (Ba, Fe, Mn)-oxides revealed that both Fe and Mn cations are in a trivalent state. Thus, it is assumed that Mn3+ can partially be substituted for Fe3+ in barium hexaferrites.
Institute für Anorg. Chemie, Universität Bonn, 53117 Bonn, Germany. herbert.schmid@uni-bonn.de
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