Compositional effects on densification and microstructural evolution of bismuth titanate

The effects of small compositional variations on the densification and microstructural evolution of bismuth titanate (Bi4Ti3O12) powder compacts were investigated during sintering and during hot forging. For a nominally stoichiometric Bi4Ti3O12 composition, sintering commenced at ∼870°C, leading to a relatively dense microstructure (relative density >97% of the theoretical value) with randomly aligned elongated grains after 1 h at 1100°C. Small additions (1 weight percent) of Bi2O3 or TiO2 to the nominally stoichiometric Bi4Ti3O12 composition shifted the onset of sintering to lower or higher temperatures, respectively, but did not significantly alter the final density. Hot forging produced a microstructure of aligned, elongated grains. The small compositional variations did not seriously influence the ability to develop the elongated grain alignment. However, subsequent annealing of the hot forged materials produced significant changes in the aligned grain microstructure. The elongated grain alignment in the nominally stoichiometric Bi4Ti3O12 composition was destroyed during subsequent annealing for less than 2 h at 1100°C.