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 100nm. The average grain size was 1.6 mu m and the biggest one was controlled less than 3 mu m. Dielectric constant around epsilon(T)(r33) of the poled samples was 5000 and electromechanical coupling factor k(P) was 42%. Large piezoelectric constants d(33) = 460 pC/N and d(31) = - 185 pC/N were measured by a d(33)-meter and the resonance-antiresonance method, respectively. A high Poisson's ratio sigma = 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 d(33) of the ceramics. The discovery of high d(33) in non-lead-based BaTiO3 ceramics with low cost process has important practical consequences in addition to scientific interest.