Characterization of nanocrystalline manganese oxide powder prepared by inert gas condensation

Nanocrystalline manganese oxide powders were synthesized by an inert gas condensation technique. The manganese oxide powders, prepared from vaporized metallic manganese in a helium pressure of 10 mbar, then oxidized under the oxygen pressures of 50 and 100 mbar, exhibited a mixture of β-Mn, MnO and Mn3O4 phases. X-ray diffractometry (XRD) analysis identified the predominant oxide formation of the as-prepared powder to be the phase of MnO. In situ synchrotron XRD and differential scanning calorimetry (DSC) data showed that synthesized manganese powder converts from β-Mn to MnO in the temperature range of 150–250 °C and subsequently converts to Mn3O4 above 250 °C. Transmission electron microscopy examinations confirmed that oxidation starts from the surface of the condensed β-Mn particles. Detailed valance variations of manganese of the resulting powders were investigated by synchrotron X-ray absorption spectroscopy techniques.