shows microstructure developments of silica-coated BaTiO3 powders at various levels. There was observed some discernible progress as the SiO2 content increased. The powder agglomeration decreased with increasing silica content. At 5.0 wt.% SiO2, the powder exhibits a uniform distribution without agglomeration. This disappearance of agglomeration could be due to the electrostatic repulsion between the coated silica layers on the surface of BaTiO3 particles.
Zeta potential of uncoated BaTiO3 particles and 5 wt.% SiO2-coated particles are plotted as a function of pH in Fig. 3. The electrophoretic mobility was measured as a function of pH values. Above pH 3.0, the zeta potential of the coated BaTiO3 is more negative than that of the uncoated BaTiO3, indicating that the coated specimen is more negatively charged than the uncoated one. This result is similar to the previous report that the zeta potential of silica-coated BaTiO3 is close to that of pure silica and more negative than that of the uncoated BaTiO3[14]. This is compatible with the morphology of 5 wt.% SiO2-coated BaTiO3 SEM images shown in Fig. 2(e), where the heavy agglomeration of primary particles disappeared. It is thus confirmed that silica coating could modify the surface characteristics of BaTiO3 nano powders and improve the dispersion of BaTiO3 primary particles.