A rapid one-step mechanosynthesis and characterization of nanocrystalline CaFe2O4 with orthorhombic structure

CaFe2O4 nanopowders were prepared via single-step mechanochemical processing of two various mixtures of precursors: simple oxides (CaO and α-Fe2O3) and elemental metal and oxide powders (Ca and α-Fe2O3). The mechanically induced evolution of the CaO/α-Fe2O3 and Ca/α-Fe2O3 mixtures was followed by 57Fe Mössbauer spectroscopy, XRD, and HR-TEM. The mechanosynthesis of CaFe2O4 proceeds very rapidly if starting from the metal/oxide system; after only 1 h of the mechanochemical treatment performed at room temperature, the synthesis of the complex oxide is almost completed. This is in a strong contrast to the conventional solid-state synthesis of CaFe2O4, which requires prolonged exposure (∼20 h) at considerably elevated temperatures (∼1400 K). It was revealed that mechanosynthesised CaFe2O4 nanoparticles with an average size of about 15 nm possess the core–shell structure consisting of an ordered inner core surrounded by a disordered surface shell with the thickness of about 1.9 nm. The main structural features of the surface shell of nanoparticles are distorted oxygen octahedra.