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

Abstract

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 εr33T of the poled samples was 5000 and electromechanical coupling factor kp 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.