Novel sol-gel method for low temperature synthesis of nanostructured Mn3O4: Structure, cation valence states, optical and electrical properties

Novel low temperature sol-gel route for the synthesis nanostructured Hausmannite, Mn3O4 with very small crystallite size (9 +/- 1 nm) and phase purity is reported. Reaction temperature of 0-5 degrees C and drying temperature of 40 degrees C is the lowest reported so far. Average particle size (8 +/- 1 nm) measured from Transmission Electron Microscopy is in good agreement with the crystallite size indicating monodispersed nature. Raman analysis indicates the presence of +4 valence states for Mn over and above +2 and +3 and the presence of an Mn2O3 like surface layer. XPS analysis confirms the phase purity as well as the presence of Mn4+ ions. Presence of +4 valence state for Mn is attributed to the presence of cation vacancies that lead to disproportionate reactions. UV-visible absorption spectra is quite broad with charge transitions associated with Mn2+, Mn3+ and Mn4+ states and d-d crystal field transitions. DC electrical conductivity is about two orders of magnitude higher than that of single crystalline Mn3O4 and the conduction mechanism is defect dependent.

Automated summary

The report describes a novel low temperature sol-gel method for synthesizing nanostructured Hausmannite, Mn3O4, with very small crystallite size and high phase purity. Analysis using Raman and XPS confirms the presence of Mn in a +4 valence state and the purity of the phase. UV-visible absorption spectra show broad charge transitions associated with different Mn valence states, while DC electrical conductivity is significantly higher compared to single crystalline Mn3O4.