Synthesis, Cation Distribution and Crystal Structure of the Spinel Oxides Zn_xMn_1-xFeCrO₄ (0.2≤x≤0.8) by Neutron Diffraction

The spinel oxides Zn_xMn_1-xFeCrO₄ (x=0.2, 0.4, 0.6 and 0.8) were obtained by solid state sintering technique in air at 1300°C. X-ray and neutron powder diffraction measurements have been performed on the samples at room temperature (RT) in order to characterize the materials. X-ray diffraction patterns showed sharp peaks indicating the formation of single phase cubic spinel structure for all the samples. Rietveld refinement of the neutron diffraction data reveals that all the samples of the series possess cubic symmetry corresponding to the space group F d-3m. The distribution of the four cations Zn, Mn, Fe and Cr over the two sublattices and other crystallographic parameters have been determined precisely from the analysis of neutron diffraction data. Fe and Mn ions are distributed over both the tetrahedral (A) and octahedral (B) sites, while Zn and Cr ions invariably occupy the A and B sites, respectively. However, the occupation of Fe ions decreases in A site and increases in B site, while Mn ions decreases in both the sites with increasing x. The lattice constant and the oxygen position parameter decrease with increasing Zn content. The decrease of tetrahedral and octahedral bond distances with x was also revealed from the refinement. Sublattices and net magnetic moments were deduced from the refinement of neutron diffraction data. The magnetic structure at room temperature was found to be ferrimagnetic for the samples x≤0.6 with no remarkable magnetic moments at x=0.8. (author)