Exaggerated Growth of Hexagonal Barium Titanate under Reducing Sintering Conditions

The influence of reducing sintering conditions on anisotropic grain growth in BaTiO₃ was studied above the BaTiO₃-Ba₆Ti₁₇O₄₀ eutectic temperature. The morphology and structure of exaggeratedly grown grains was examined by X-ray powder diffractometry, scanning electron micros-copy, and high-resolution transmission electron microscopy. The results show that all anomalously grown anisotropic grains were hexagonal BaTiO₃ in the form of platelike crystals with a/c ratios up to 10. The direction of preferential growth of hexagonal grains is crystallographically analogous with that of parallel (111) twins in a cubic phase. Ti³⁺ ions, induced by reducing atmosphere, play an important role in the formation of hexagonal stacking.