Anisotropic grain growth of Bi4Ti3O12 in molten salt fluxes

Bismuth titanate (Bi4Ti3O12) platelets were obtained by the molten salt synthesis method in NaCl–KCl and Na2SO4–K2SO4 fluxes, using an amorphous Bi4Ti3O12 precursor and a mechanically mixed Bi2O3–TiO2 mixture as the starting materials. It was found that the synthesizing temperature, salt species and starting materials could significantly affect the crystallization habit and morphology of Bi4Ti3O12 platelets. Under the same processing conditions (i.e. in Na2SO4–K2SO4 flux at 1000 °C), the Bi4Ti3O12 platelets synthesized from the Bi2O3–TiO2 mixture generally showed a smaller particle size than those synthesized using the amorphous Bi4Ti3O12 precursor. The Bi4Ti3O12 platelets prepared in the chloride flux were faceted along either (0 0 1) or (1 1 2) planes, while those prepared in the sulfate flux were solely (0 0 1) faceted. The former system also had smaller particle size than the latter. Furthermore, the salt content and the addition of plate-like Bi4Ti3O12 seeds in the amorphous Bi4Ti3O12 precursor showed a strong influence on the particle size of the synthesized Bi4Ti3O12 platelets. The particle size of Bi4Ti3O12 platelets prepared in the sulfate flux decreased as the mole ratio of the sulfate salts to Bi4Ti3O12 was increased from 7.9 to 23.7. And the addition of 10 wt.% plate-like Bi4Ti3O12 seeds into the amorphous Bi4Ti3O12 precursor led to a significant increase in the particle size of the resulting Bi4Ti3O12 platelets.