Characterization of acceptor-doped (Ba, Ca)TiO3 “hard” piezoelectric ceramics for high-power applications

Acceptor Mn or Co-doped Ba0.925Ca0.075TiO3 (abbreviated as BCT-Mn and BCT-Co) lead-free piezoelectric ceramics with high density and fine grains were synthesized by conventional solid-state reaction method. The phase structure and electrical properties of the ceramics were investigated. The acceptor-doped BCT ceramics were found to exhibit asymmetrical polarization-electric field hysteresis loops corresponding to the presence of an internal bias field Ei, indicating that the domain walls were pinned by preferentially oriented defect dipoles formed by the acceptors and oxygen vacancies. High mechanical quality factor Qm and low dielectric loss tanδ were obtained for the ceramics due to the strong internal bias field (Ei =4-5kV/cm). In particular, BCT-Mn ceramics exhibited the best properties, with mechanical quality factor Qm =1020, dielectric loss tanδ=0.2% and piezoelectric coefficient d33 =190 pC/N. Furthermore, the planar electromechanical coupling factor kp for BCT-Mn ceramics was found to be larger than 0.4 in the temperature range of 25 °C to 75 °C. These results indicate that the Mn-doped BCT lead-free ceramics material is a promising candidate for high-power piezoelectric applications.