Thermal stability and structural transition of metastable Mn5O8: in situ micro-Raman study

The Raman spectrum of the metastable Mn5O8 phase, obtained from slow oxidat ion of Mn3O4 at low temperature, is presented and analysed for the first ti me and the thermal stability is monitored by the changes in Raman spectra d ue to laser-induced thermal treatments. A structural transformation toward the spinel phase Mn3O4 is observed at temperature higher than 1000 K. Other Mn oxides, characterised by intermediate Mn oxidation states, are not dete cted below or during the transition. A compositional model of the sample gr ains is also proposed by comparing Raman data with X-ray diffraction and sc anning electron microscopy measurements. (C) 1999 Elsevier Science Ltd. All rights reserved.