Ferroelectric hollow particles obtained by solid-state reaction

Hollow particles of barium titanate were obtained by a two-step process combining colloidal
chemistry and solid-state reaction. BaCO3 crystals (size ~1µm) suspended in a peroxy-Ti(IV)
aqueous solution were coated with an amorphous TiO2 shell using a precipitation process.
Calcination of the BaCO3@TiO2 core-shell particles at 700 °C resulted in the formation of
BaTiO3 hollow particles (shell thickness of ~70 nm) which retain the morphology of the
BaCO3 crystals. Formation of the cavity occurs because out-diffusion of the core phase is much
faster than in-diffusion of the shell material. X-ray diffraction (XRD) and Raman spectroscopy
indicate that the hollow particles possess a tetragonal ferroelectric structure with axial ratio
c/a = 1.005. Piezoresponse force microscopy has shown strong piezoactivity and 180°
ferroelectric domains. The process described provides a general route to fabricate hollow
ferroelectric structures of several compounds.