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 alpha-Fe2O3) and elemental metal and oxide powders (Ca and alpha-Fe2O3). The mechanically induced evolution of the CaO/alpha-Fe2O3 and Ca/alpha-Fe2O3 mixtures was followed by Fe-57 Mossbauer 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 (similar to 20 h) at considerably elevated temperatures (similar to 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. (C) 2010 Elsevier B.V. All rights reserved.