Preparation of a-b plane oriented Nb-doped Bi4Ti3O12 ceramics by magnetic alignment via gelcasting

Highly a-b plane grain-oriented Nb-doped Bi4Ti3O12 ceramics (Bi4Ti2.96Nb0.04O12, BINT) were successfully prepared by magnetic alignment (MA) via gelcasting technique using only conventional solid-state-synthesized starting powder. The micro-size BINT particles with irregular shape were aligned in slurry by strong magnetic force and then in situ locked by polymerization via gelcasting technique in 30 min in a 10 T magnetic field. Highly a-b plane orientation parallel to the magnetic field direction (//B) was obviously observed in the green compact (f(200)/(020) = 0.41) and sintered sample (f(200)/(020) = 0.67). The sintered sample contained plate-like grains and reached 97% theoretical density. Compared to the controlled sample without magnetic alignment, the magnetically aligned sample shows enhanced dielectric constant in //B direction (160 versus 120 at room temperature and 350 versus 250 at 580 °C). This method, using typical gelcasting technique in a strong magnetic field, readily applicable to prepare other ceramics and is expected to facilitate the mass preparation of large and dense grain-oriented ceramic components.