Subgrain Microstructure in High-Performance BaTiO₃ Piezoelectric Ceramics

We have successfully observed subgrains of 1 µm average size in large grains (1 to 10 µm) in high-performance barium titanate (BaTiO₃) piezoelectric ceramics manufactured by two-step sintering. The BaTiO₃ ceramics fabricated from hydrothermally synthesized BaTiO₃ with an average particle size of 0.1 µm had a density = 5.93 g/cm³, an electromechanical coupling factor k_p = 50%, and a piezoelectric constant d₃₃ = 500 pC/N, which are the highest values reported thus far. Subgrain boundaries were considered to have a lower energy than main-grain boundaries. The subgrain structure restricted ferroelectric domain growth resulting in a nanosized domain structure, a large k_p and a large d₃₃. These features have important practical implications in addition to the scientific interest they generate in the fabrication of lead-free high-performance piezoelectric ceramics.