A general approach to monodisperse perovskite microspheres

BaTiO₃, PbTiO₃, SrTiO₃, and Pb(Zr,Ti)O₃ microspheres with uniform size and narrow size distribution have been successfully synthesized by a novel hydrothermal and annealing approach. In this approach, the chemical reaction and crystallization process of the ABO₃ perovskite oxides were separated in two steps. Spherical particles containing the B-site ions were obtained first via a controlled hydrolysis and aging process. Then, during hydrothermal treatment, the A-site ions were incorporated in situ into the microspheres to form amorphous perovskite microspheres. The particles were further crystallized with preserved spherical morphology under subsequent annealing treatment. The BET surface areas of the TiO₂ gel particles, the amorphous PbTiO ₃ and the as-annealed PbTiO₃ microspheres were 245.7 m²/g, 41.67 m²/g and 4.53 m²/g, respectively, showing a significant change of the surface feature in the preparation process. This approach also allowed the microspheres diameters to be manipulated from 100 nm to 1500 nm in a controlled manner. Most of the microspheres were composed by closely packed nano-sized particles. Furthermore, the Pb(Zr,Ti)O₃ microspheres with an average diameter of 200 nm exhibited single crystal features, indicating highly oriented growth in the crystallization process. The microspheres were very stable, and still maintained spherical shape after higher temperature calcination.