Formation mechanism and magnetic properties of three different hematite nanostructures synthesized by one-step hydrothermal procedure

The spindle-like, tubular, and tire-like hematite were successively fabricated by a facile, one-step hydrothermal procedure, which is of great importance in facilitating the controllable-synthesis process of commercial industrialization. A mechanism involving a formation-dissolution process was proposed based on the X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and high-resolution transmission electron microscopy analysis. It was demonstrated that the presence of phosphate ions during the reaction process is crucial to the morphology evolution of hematite. Their different adsorption ability on the different crystallographic planes of hematite and a coordination effect with ferric ions could promote the preferential dissolution of the spindle-like hematite precursors along the long axis [001] from the tips down to the interior, and thus yield the tubular and tire-like hematite one by one with the increasing reaction time. The magnetic measurements have also been performed to investigate the different magnetic properties such as coercivity and low-temperature transition behavior of three different hematite nanostructures.