Oxidation states of Mn and Fe in various compound oxide systems

Energy-loss near-edge structure (ELNES) data of Mn-L-2,L-3 and Fe-L-2,L-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,L-3 and Fe-L-2,L-3 white-lines, as well as the white-line intensity ratio (L-3/L-2) vary with cation oxidation states. Additionally, spin-orbit spitting, i.e. the energy difference AE(L-2-L-3) between Mn-L-2,L-3 white-lines decreases with increasing Mn oxidation state. With these data from known standards calibration curves on white-line intensity ratio Mn(L-3/L-2) vs. Mn oxidation state, and Fe(L-3/L-2) 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,L-3 and Fe-L-2,L-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. (c) 2006 Elsevier Ltd. All rights reserved.