ELECTRON-BEAM-INDUCED REDUCTION OF MN4+ IN MANGANESE OXIDES AS REVEALED BY PARALLEL EELS

Chemical reduction of Mn4+ in the mineral asbolan was examined using parallel electron energy-loss spectroscopy (PEELS). Changes in the oxidation state of the manganese were monitored by recording the electron energy-loss near-edge structure (ELNES) for the Mn M(2,3-) and L(2,3-)edges. The edges in the undamaged material were consistent with Mn4+. Electron beam irradiation of the mineral caused the ionisation edges to change in shape and energy consistent with the decrease in the proportion of the Mn4+ and the increase in the proportions of Mn3+ and Mn2+. The final edge is very similar in energy and shape to that of Mn2+ in rhodochrosite (MnCO3) and manganosite (MnO) and the differences in shape can be accounted for by the presence of a small amount of residual Mn3+.