Nanospheres of Silica with an ε-Fe₂O₃ Single Crystal Nucleus

A route to produce single crystals of ε-Fe2O3 individually wrapped in a silica shell is presented. Formation of ε-Fe2O3/silica nanospheres was achieved by controlled recrystallization of maghemite particles confined in silica shells via calcination in air. Phase transition was monitored by X-ray diffraction, magnetometry, and transmission electron microscopy. Core−shell nanocomposite particles can be dispersed as a colloidal suspension in several polar liquids enlarging the processability spectrum of the material and thus facilitating the use of ε-Fe2O3 in technological applications and its integration in devices.