Controlled Growth of Silica Shell on Ba_0.6Sr_0.4TiO₃ Nanoparticles Used As Precursors of Ferroelectric Composites

A method based on a seeded growth process was developed to coat ferroelectric nanoparticles with a dielectric silica shell. This method, applied to size-polydispersed (Ba 0.6 Sr 0.4 )TiO 3 particles (BST, mean diameter 150 nm), allows the control of the silica shell thickness from 2 to 80 nm with an accuracy of 1−2 nm. The morphology and surface physical chemistry of the core−shell were studied by transmission electron microscopy, photon correlation spectroscopy, and zeta potential measurements. A size-sorting procedure consisting of several cycles of centrifugation was optimized to extract the BST@silica nanoparticles of the required size for dielectric properties tuning. Upon sintering, dielectric measurements showed that the ferroelectric transition was maintained in the dense nanocomposites.