Anisotropic grain growth of Bi4Ti3O12 in molten salt fluxes

Abstract Bismuth titanate (Bi 4 Ti 3 O 12 ) platelets were obtained by the molten salt synthesis method in NaCl–KCl and Na 2 SO 4 –K 2 SO 4 fluxes, using an amorphous Bi 4 Ti 3 O 12 precursor and a mechanically mixed Bi 2 O 3 –TiO 2 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 Bi 4 Ti 3 O 12 platelets. Under the same processing conditions (i.e. in Na 2 SO 4 –K 2 SO 4 flux at 1000 °C), the Bi 4 Ti 3 O 12 platelets synthesized from the Bi 2 O 3 –TiO 2 mixture generally showed a smaller particle size than those synthesized using the amorphous Bi 4 Ti 3 O 12 precursor. The Bi 4 Ti 3 O 12 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 Bi 4 Ti 3 O 12 seeds in the amorphous Bi 4 Ti 3 O 12 precursor showed a strong influence on the particle size of the synthesized Bi 4 Ti 3 O 12 platelets. The particle size of Bi 4 Ti 3 O 12 platelets prepared in the sulfate flux decreased as the mole ratio of the sulfate salts to Bi 4 Ti 3 O 12 was increased from 7.9 to 23.7. And the addition of 10 wt.% plate-like Bi 4 Ti 3 O 12 seeds into the amorphous Bi 4 Ti 3 O 12 precursor led to a significant increase in the particle size of the resulting Bi 4 Ti 3 O 12 platelets.