Electrical Performance of Non-Stoichiometry Manganese Oxides

Manganese oxides have been receiving considerable attention because of their performance as catalyst, and energy storage materials. Among them, hausmanite (Mn3O4) and bixbyite (Mn2O3) type of materials are used for catalytical reaction in which electron transfer reactions are involved. Several studies focus on their catalytic properties, but less attention has been paid to their electrical properties. In this work, Mn3O4 and Mn2O3 were prepared with thermal oxidation of manganese acetate at 400 °C, 600 °C and 800 °C. The XPS and XRD results revealed the formation of Mn3O4 at 400 °C, and a Mn2O3 type of structure for 600 °C and 800°C. Rietveld refinement of these structures revealed a tetragonal unit cell structure for the Mn3O4 and cubic phase for Mn2O3. Electrical analysis by impedance spectroscopy showed a mixed conductor behavior for Mn3O4 since the conductivity depended on the frequency of the electric field. For the Mn3O4 phases at 400 °C and Mn2O3 synthesized at 600 °C and 800 °C the bulk conductivities were 3,871 x 10-8 Ω-1cm-1, 9,850 x 10-8 Ω-1cm-1, 16,790 x 10-8 Ω-1cm-1 respectively, indicating strong influence of the crystallographic phase and cellular parameter. The DFT calculations corroborate the influence of the crystalline structure on the electrical behavior of the materials studied. Furthermore, a dielectric relaxation process was presented for Mn2O3, suggesting vacancies and the orientation of the local dipoles in this type of structures. •Hausmannite an bixbyite were synthesized for thermal oxidation•XPS supports the presence of oxygen vacancies, also DFT•The AC electrical conductivity is higher for bixbyite than hausmannite.•Electron hopping is the main mechanism to electron conduction.