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Manganese(III) oxide
Chemical compound From Wikipedia, the free encyclopedia
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Manganese(III) oxide is a chemical compound with the formula Mn2O3. It occurs in nature as the mineral bixbyite (recently changed to bixbyite-(Mn)[3][4]) and is used in the production of ferrites and thermistors.
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Preparation and chemistry
Heating MnO2 in air at below 800 °C produces α-Mn2O3 (higher temperatures produce Mn3O4).[5] γ-Mn2O3 can be produced by oxidation followed by dehydration of manganese(II) hydroxide.[5] Many preparations of nano-crystalline Mn2O3 have been reported, for example syntheses involving oxidation of MnII salts or reduction of MnO2.[6][7][8]
Manganese(III) oxide is formed by the redox reaction in an alkaline cell:
- 2 MnO2 + Zn → Mn2O3 + ZnO[citation needed]
Manganese(III) oxide Mn2O3 must not be confused with MnOOH manganese(III) oxyhydroxide. Contrary to Mn2O3, MnOOH is a compound that decomposes at about 300 °C to form MnO2.[9]
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Structure
Mn2O3 is unlike many other transition metal oxides in that it does not adopt the corundum (Al2O3) structure.[5] Two forms are generally recognized, α-Mn2O3 and γ-Mn2O3,[10] although a high pressure form with the CaIrO3 structure has been reported too.[11]
α-Mn2O3 has the cubic bixbyite structure, which is an example of a C-type rare earth sesquioxide (Pearson symbol cI80, space group Ia3, #206). The bixbyite structure has been found to be stabilised by the presence of small amounts of Fe3+, pure Mn2O3 has an orthorhombic structure (Pearson symbol oP24, space group Pbca, #61).[12] α-Mn2O3 undergoes antiferromagnetic transition at 80 K. [13]
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.[10] γ-Mn2O3 is ferrimagnetic with a Néel temperature of 39 K.[14]
ε-Mn2O3 takes on a rhombohedral ilmenite structure (the first binary compound known to do so), wherein the manganese cations divided equally into oxidation states 2+ and 4+. ε-Mn2O3 is antiferromagnetic with a Néel temperature of 210 K.[15]
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References
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