Structural Stability and Properties of Marokite-Type γ-Mn3O4

We synthesized single crystals of marokite (CaMn2O4)-type orthorhombic manganese (II,III) oxide, gamma-Mn3O4, in a multianvil apparatus at pressures of 10-24 GPa. The magnetic, electronic, and optical properties of the crystals were investigated at ambient pressure. It was found that gamma-Mn3O4 is a semiconductor with an indirect band gap E-g of 0.96 eV and two antiferromagnetic transitions (TN) at similar to 200 and similar to 55 K. The phase stability of the gamma-Mn3O4 crystals was examined in the pressure range of 0-60 GPa using single-crystal X-ray diffraction and Raman spectroscopy. A bulk modulus of gamma-Mn3O4 was determined to be B-0 = 235.3(2) GPa with B' = 2.6(6). The gamma-Mn3O4 phase persisted over the whole pressure range studied and did not transform or decompose upon laser heating of the sample to similar to 3500 K at 60 GPa. This result seems surprising, given the high-pressure structural diversity of iron oxides with similar stoichiometries. With an increase in pressure, the degree of distortion of MnO6 polyhedra decreased. Furthermore, there are signs indicating a limited charge transfer between the Mn3+ ions in the octahedra and the Mn2+ ions in the trigonal prisms. Our results demonstrate that the high-pressure behavior of the structural, electronic, and chemical properties of manganese oxides strongly differs from that of iron oxides with similar stoichiometries.

Automated summary

In this study, single crystals of marokite-type orthorhombic manganese oxide gamma-Mn3O4 were synthesized at high pressures. The semiconductor material exhibited two antiferromagnetic transitions and remained stable under high pressures, unlike similar iron oxides. The research highlighted significant differences in the high-pressure behavior of manganese oxides compared to iron oxides with similar stoichiometries.