Manganese(III) oxide
Manganese(III) oxide is a chemical compound with the formula MnO. It occurs in nature as the mineral braunite, and is used in the production of ferrites and thermistors. Preparation and chemistry. Heating MnO in air at below 800 °C produces α-MnO (higher temperatures produce MnO). γ-MnO can be produced by oxidation followed by dehydration of manganese(II) hydroxide. Many preparations of nano-crystalline MnO have been reported, for example syntheses involving oxidation of Mn salts or reduction of MnO. Manganese(III) oxide is formed by the redox reaction in an alkaline cell: Manganese(III) oxide MnO must not  be confused with MnOOH manganese(III) oxyhydroxide. Contrary to MnO, MnOOH is a compound that decomposes at about 300 °C to form MnO. Structure. MnO is unlike many other transition metal oxides in that it does not adopt the corundum (AlO) structure. Two forms are generally recognized, α-MnO and γ-MnO, although a high pressure form with the CaIrO structure has been reported too. α-MnO has the cubic bixbyite structure, which is an example of a C-type rare earth sesquioxide (Pearson symbol cI80, space group Ia, #206). The bixbyite structure has been found to be stabilised by  the presence of small amounts of Fe, pure MnO has an orthorhombic structure (Pearson symbol oP24, space group Pbca, #61). α-MnO undergoes antiferromagnetic transition at 80 K. γ-MnO has a structure related to the spinel structure of MnO where the oxide ions are cubic close packed. This is similar to the relationship between γ-FeO and FeO. γ-MnO is ferrimagnetic with a Néel temperature of 39 K.