Lead-Free Piezoelectric Ceramics with Large Dielectric and Piezoelectric Constants Manufactured from BaTiO₃ Nano-Powder

Barium titanate (BaTiO₃) ceramics with a density of more than 98% of the theoretical value were fabricated by two-step sintering method from hydrothermally synthesized BaTiO₃ nano-particles of 100 nm. The average grain size was around 1.6 µm and the biggest one was controlled less than 3 µm. Dielectric constant ε_r33^T of the poled samples was 5000 and electromechanical coupling factor k_p was 42%. Large piezoelectric constants d₃₃ = 460 pC/N and d₃₁ = -185 pC/N were measured by a d₃₃-meter and the resonance–antiresonance method, respectively. A high Poisson's ratio σ= 0.38 was determined from the ratio of overtone frequency and resonant frequency in the planar mode. The high Poisson's ratio and the large dielectric constants are most likely the origin of the high d₃₃ of the ceramics. The discovery of high d₃₃ in non-lead-based BaTiO₃ ceramics with low cost process has important practical consequences in addition to scientific interest.