Nearly monodisperse ferroelectric BaTiO₃ hollow nanoparticles: Size-related solid evacuation in ostwald-ripening-induced hollowing process

Nearly monodisperse BaTiO₃ hollow nanoparticles were prepared through a one-pot template-free route in molten hydrated salt medium. The composition and morphologies of the time-dependent products were investigated in detail, and Ostwald ripening is concluded to be responsible for the hollowing evolvement of the BaTiO₃ particles. The size of the initial solid particles is proposed to play an important role in determining the evacuation manner of the solid in the ripening-induced hollowing process, that is, evacuating from the center region or underneath the surface layer of the solid aggregates, and could result in the morphology variation (i.e., hollow geometry or core-shell one) of the final products. Our study also points out that a highly active precursor is crucial to improve the uniformity of the products, and elevated reaction temperature is a prerequisite to activate the hollowing evolvement of solid aggregates. Second-harmonic-generation and Raman analyses revealed the ferroelectric tetragonal characteristic of the obtained BaTiO ₃ hollow nanoparticles, and the tetragonality (c/a) was quantified to be about 1.005 according to the Rietveld refinement of the X-ray diffraction pattern.