Investigation of LaFeO3 perovskite growth mechanism through mechanical ball milling of lanthanum and iron oxides

LaFeO3 perovskite was synthesized mechanochemically through ball milling of La2O3 and Fe2O3 in stoichiometric ratio. X-ray powder diffraction (XRPD), simultaneous differential scanning calorimetry and thermogravimetry analysis (DSC–TGA), Mossbauer spectroscopy, scanning electron microscopy (SEM), and optical diffuse reflectance spectroscopy were combined for a detailed study of the growth mechanism of LaFeO3 perovskite during the ball milling process. The XRPD results showed that La2O3 is unstable when exposed to air. Both La2O3 and La(OH)3 phases coexist under the ball milling process, indicating that La2O3 or La(OH)3 can be used to produce LaFeO3. The formation of LaFeO3 perovskite was evident after only 2 h of milling and the amount of LaFeO3 gradually increased with the increase of ball milling time. After 12 h of ball milling, single phase LaFeO3 was formed. The Mossbauer spectroscopy studies show that the spectrum of the formed LaFeO3 phase consists of three sextets and one doublet, indicating the wide distribution of LaFeO3 particle sizes and some of the smaller particles having superparamagnetic properties. This is in good agreement with the SEM images, which show that the formed LaFeO3 phase consists of nanometer-sized particles and micrometer-sized agglomerates. The formation of LaFeO3 phase was mainly caused by the La3+ substitution of Fe3+ in Fe2O3 lattice. Optical diffuse reflectance spectroscopy studies show that the formed LaFeO3 phase has semiconductor properties, with the band gap energy ~2.67 eV.