Self-propagating high-temperature synthesis of lithium-chromium ferrites Li0.5Fe2.5-xCrxO4

Abstract

Pure and chromium-substituted lithium ferrites have been made in air by self-propagating high-temperature synthesis (SHS), a combustion process involving the reaction of lithium peroxide, iron oxide, chromium oxide and iron or chromium metal powders. Three series of SHS samples were produced: by SHS only; by SHS followed by sintering at C for 2 h; and by SHS in a magnetic field of 1.1 T followed by sintering at C for 2 h. X-ray data showed that a cubic spinel ferrite was produced in all cases, with single-phase products achieved after sintering. Systematic changes in lattice parameter were seen both as a function of Cr content and, for the sintered samples, as a result of the field applied during SHS. Scanning electron microscopy showed that the crystallites had sizes of order . Electron microprobe analysis and EDAX indicated that the samples were homogeneous and had the expected Fe-to-Cr ratios. Mössbauer and magnetic hysteresis data showed that there were significant changes in sublattice occupancy and nett magnetization with Cr content. Coercive forces in the Cr-doped ferrites were larger than those in pure compositions. Some differences between Mössbauer and magnetization parameters of the sintered zero-field and applied-field SHS samples were observed.