Mössbauer studies on cation distribution and lattice distortion in magnesium manganites

Mössbauer studies are reported on a magnesium manganite series Mg_xMn_2.9?xFe_0.1O₄ for 0.5 ? x ? 2.4. In the region x ? 1.4 two quadrupole doublets are observed while for x ? 1.8 only one doublet could be observed. Quadrupole splitting (QS) has been studied as a function of x and an unusually large QS for the outer doublet has been attributed to Jahn-Teller distortion whose onset has been located in the region 1.8 > x > 1.4; this is corroborated by X-ray diffraction studies. Probable cation distributions are proposed. Oxygen ion parameters are estimated for the compositions corresponding to x = 1 (tetragonal phase) and x = 2 (cubic phase) under point charge approximation for electric field gradient at Fe³⁺ sites.