Manganese(III) oxide is a chemical compound with the formula Mn₂O₃. It occurs in nature as the mineral

bixbyite Bixbyite is a manganese iron oxide mineral with chemical formula: (Mn,Fe)2O3. The iron/manganese ratio is quite variable and many specimens have almost no iron. It is a metallic dark black with a Mohs hardness of 6.0 - 6.5. It is a somewhat rare ...

(recently changed to bixbyite-(Mn)IMA 21-H: Redefinition of bixbyite and definition of bixbyite-(Fe) and bixbyite-(Mn). CNMNC Newsletter, 64, 2021; Mineralogical Magazine, 85, 2021).) and is used in the production of ferrites and

thermistor A thermistor is a type of resistor whose resistance is strongly dependent on temperature, more so than in standard resistors. The word thermistor is a portmanteau of ''thermal'' and ''resistor''. Thermistors are divided based on their conduction ...

Preparation and chemistry

Heating MnO₂ in air at below 800 °C produces α-Mn₂O₃ (higher temperatures produce Mn₃O₄). 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 Mn^II salts or reduction of MnO₂. Manganese(III) oxide is formed by the redox reaction in an alkaline cell: : 2 MnO₂ + Zn → Mn₂O₃ + ZnO 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.

Structure

Mn₂O₃ is unlike many other transition metal oxides in that it does not adopt the

corundum Corundum is a crystalline form of aluminium oxide () typically containing traces of iron, titanium, vanadium and chromium. It is a rock-forming mineral. It is a naturally transparent material, but can have different colors depending on the pres ...

( Al₂O₃) structure. Two forms are generally recognized, α-Mn₂O₃ and γ-Mn₂O₃,Wells A.F. (1984) ''Structural Inorganic Chemistry'' 5th edition Oxford Science Publications although a high pressure form with the CaIrO₃ structure has been reported too. α-Mn₂O₃ has the cubic

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 Fe³⁺, pure Mn₂O₃ has an orthorhombic structure ( Pearson symbol oP24, space group Pbca, #61). α-Mn₂O₃ undergoes

antiferromagnetic In materials that exhibit antiferromagnetism, the magnetic moments of atoms or molecules, usually related to the spins of electrons, align in a regular pattern with neighboring spins (on different sublattices) pointing in opposite directions. ...

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 A ferrimagnetic material is a material that has populations of atoms with opposing magnetic moments, as in antiferromagnetism, but these moments are unequal in magnitude so a spontaneous magnetization remains. This can for example occur when ...

with a

Néel temperature In physics and materials science, the Curie temperature (''T''C), or Curie point, is the temperature above which certain materials lose their permanent magnetic properties, which can (in most cases) be replaced by induced magnetism. The Cur ...

of 39 K. ε-Mn₂O₃ takes on a rhombohedral

ilmenite Ilmenite is a titanium-iron oxide mineral with the idealized formula . It is a weakly magnetic black or steel-gray solid. Ilmenite is the most important ore of titanium and the main source of titanium dioxide, which is used in paints, printing ...

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.

References

{{oxides Manganese(III) minerals Sesquioxides Transition metal oxides