HIGH-RESOLUTION PARALLEL ELECTRON-ENERGY-LOSS SPECTROSCOPY OF MN L(2,3)-EDGES IN INORGANIC MANGANESE COMPOUNDS

Parallel electron energy-loss spectroscopy (PEELS) in a scanning trans mission electron microscope (STEM) was used to record the Mn L2,3-edge s from a range of natural and synthetic manganese containing materials , covering valences 0, II, III, IV and VII, with an energy resolution of ca. 0.5 eV. The Mn L2,3 electron-loss near-edge structure (ELNES) o f these edges provided a sensitive fingerprint of its valence. The Mn2 + L2,3-edges show little sensitivity to the local site symmetry of the ligands surrounding the manganese. This is illustrated by comparing t he Mn L2,3-edges from 4-, 6- and 8-fold coordinated Mn2+. In contrast, the Mn L3-edges from Mn3+ and Mn4+ containing minerals exhibited ELNE S that are interpreted in terms of a crystal-field splitting of the 3d electrons, governed by the symmetry of the surrounding ligands. The M n L3-edges for octahedrally coordinated Mn2+, Mn3+ and Mn4+ showed var iations in their ELNES that were sensitive to the crystal-field streng th. The crystal-field strength (10Dq) was measured from these edges an d compared very well with published optically determined values. The m agnitude of 10Dq measured from the Mn L3-edges and their O K-edge prep eaks of the manganese oxides were almost identical. This further confi rms that the value of 10Dq measured at the Mn L3-edge is correct. Sele cted spectra are compared with theoretical 2p atomic multiplet spectra and the differences and similarities are explained in terms of the co valency and site symmetry of the manganese. The Mn L3-edges allow the valence of the manganese to be ascertained, even in multivalent state materials, and can also be used to determine 10Dq.