The role of high-valent (Mo and V) cations in defect spinel iron oxide nanomaterials: Toward improving Li-ion storage

Abstract

Defect spinel Fe3-δO4 samples doped with high-valent Mo and V cations have been prepared by sol-gel auto-combustion rout with increasing concentrations of Mo and V, respectively. Energy Dispersive X-ray fluorescence (EDXRF) and Attenuated Total Reflection Fourier transform Infrared (ATR-FTIR) spectroscopies have verified the compositions of the samples and the oxidation states of the metal cations. Synchrotron Radiation X-ray Powder Diffraction (SR-XRPD) patterns were measured at MCX beamline of ELETTRA synchrotron. Structure and microstructure of the samples were studied by the Rietveld method. Increasing densities of vacancies were found to be generated by the high-valent Mo and V cations which were correlated to the lattice parameter, crystallite size and microstrain of each sample. The hysteresis loops were measured at room temperature using the Vibrating Sample Magnetometer (VSM) and good agreement was found between the Fe-cation distributions revealed from Rietveld adjustments and those predicted by the saturation magnetization (Ms) measurements. The High-Resolution Transmission Electron Microscopy (HRTEM) confirmed the proposed isotropic crystallite size model implemented in the Rietveld adjustments. Finally, the results presented herein show agreement with previous works on iron oxide materials used as intercalation cathode for Li-ion batteries and predict better performance for the current Mo- and V-doped defect spinel.