sStructural properties and cation distribution in a NixMn3-xO4 (0.71 <= x <= 1.0) spinel

Abstract

Cubic spinel NixMn3-xO4 (0.71 <= x <= 1) ceramics were prepared using the mixed-oxide method. The mixed powders were investigated by TG-DSC analysis in order to study the phase formation and decomposition process. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis were employed to determine the structural properties of the nickel manganite specimens, especially the distribution of manganese ions. With an increase in nickel content, both Ni2+ and Mn3+ ions predominately occupy the octahedral sites due to their preference for large octahedral site energy. The large FWHM value of the Mn 2p signals of the NiMn2O4 spinel is indicative of multiplet splitting and the charging effect is due to the presence of Mn2+, Mn3+ and Mn4+ ions. Manganese in all specimens exists in three oxidation states as Mn2+, Mn3+ and Mn4+ ions. The lattice parameter estimated from XRD decreases with an increase in Ni content due to the replacement of larger ionic radii (Mn3+) by smaller ionic radii (Ni2+).