Thermal behaviour and reactivity of manganese cobaltites MnxCo3 –xO4(0.0 ⩽x⩽1.0) obtained at low temperature

Abstract

The thermal behaviour and reactivity in air, N₂ and vacuum of manganese cobaltites Mn_xCo_{3 –x}O₄(0 ⩽x⩽1.0) with a cubic spinel-type structure obtained at low temperature have been studied by thermal analysis, X-ray powder diffraction, IR spectroscopy, transmission electron microscopy and X-ray energy-dispersive spectroscopy. In air, the formation of mixed Co–Mn oxides with rock-salt-type structure as a single phase is attained between 1100–1300 °C, depending on x. In a vacuum, the rock-salt-type mixed oxide is formed at ca. 700 ° C; Co metal and MnO are the products obtained at 800 °C. The change with temperature of the lattice constant in the cubic spinel-type phase MnCo₂O₄, has been also determined. It increases from a= 8.167(2)Å at 450 °C to 8.2626(3)Å at 950 °C. These results are interpreted with regard to the progressive reduction of manganese in the cubic spinel lattice.