Self-propagating high-temperature synthesis of lithium-chromium ferrites Li0.5Fe2.5-xCrxO4 (0≤x≤2.0)

Pure and chromium-substituted lithium ferrites Li0.5Fe2.5-xCrxO4 (0 less than or equal to x less than or equal to 2.0) 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 1150 degrees C for 2 h; and by SHS in a magnetic field of 1.1 T followed by sintering at 1150 degrees 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 1.1 mu m. Electron microprobe analysis and EDAX indicated that the samples were homogeneous and had the expected Fe-to-Cr ratios. Mossbauer 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 Mossbauer and magnetization parameters of the sintered zero-field and applied-field SHS samples were observed.