Manganese(III) oxide
Manganese oxide is a chemical compound with the formula Mn2O3. It occurs in nature as the mineral bixbyite and is used in the production of ferrites and thermistors.
Preparation and chemistry
Heating MnO2 in air at below 800 °C produces α-Mn2O3. γ-Mn2O3 can be produced by oxidation followed by dehydration of manganese(II) hydroxide. Many preparations of nano-crystalline Mn2O3 have been reported, for example syntheses involving oxidation of MnII salts or reduction of MnO2.Manganese oxide is formed by the redox reaction in an alkaline cell:
Manganese oxide Mn2O3 must not be confused with MnOOH manganese oxyhydroxide. Contrary to Mn2O3, MnOOH is a compound that decomposes at about 300 °C to form MnO2.
Structure
Mn2O3 is unlike many other transition metal oxides in that it does not adopt the corundum structure. Two forms are generally recognized, α-Mn2O3 and γ-Mn2O3, although a high pressure form with the CaIrO3 structure has been reported too.α-Mn2O3 has the cubic bixbyite structure, which is an example of a C-type rare earth sesquioxide. The bixbyite structure has been found to be stabilised by the presence of
small amounts of Fe3+, pure Mn2O3 has an orthorhombic structure. α-Mn2O3 undergoes antiferromagnetic transition at 80 K.
γ-Mn2O3 has a structure related to the spinel structure of Mn3O4 where the oxide ions are cubic close packed. This is similar to the relationship between γ-Fe2O3 and Fe3O4. γ-Mn2O3 is ferrimagnetic with a Néel temperature of 39 K.
ε-Mn2O3 takes on a rhombohedral ilmenite structure, wherein the manganese cations divided equally into oxidation states 2+ and 4+. ε-Mn2O3 is antiferromagnetic with a Néel temperature of 210 K.