Formation of Fe and Ni substituted LiMn2–XMXO4 nanopowders and their crystal and electronic structure and magnetic properties

The Pechini sol-gel method was applied to obtain LiMn_2–xT_xO₄ (T = Ni, Fe; x = 0.1 to 0.5) nanopowders. Crystal and electronic structures, chemical composition and magnetic properties of the materials were characterized by X-ray diffraction, XPS, SEM/EDX microscopy, prompt gamma-ray activation analysis (PGAA), Mössbauer spectroscopy and magnetic susceptibility, respectively. XRD measurements showed that the LiMn_2–xNi_xO₄ were single phase for x = 0.1 and 0.2. Three samples with higher Ni content contained some addition of a second phase. Analysis of the oxidation state of the dopants by XPS revealed ionic Ni²⁺ and Fe³⁺. Mössbauer spectroscopy also confirmed 3+ oxidation state of iron and its location in octahedral sites, which excluded the inverse spinel configuration. XPS examinations showed that Mn³⁺ ions dominated in the iron substituted series whereas the Mn⁴⁺ was dominant in the nickel series.