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

Acceptor Mn or Co-doped Ba_0.925Ca_0.075TiO₃ (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 E_i, indicating that the domain walls were pinned by preferentially oriented defect dipoles formed by the acceptors and oxygen vacancies. High mechanical quality factor Q_m and low dielectric loss tanδ were obtained for the ceramics due to the strong internal bias field (E_i =4–5kV/cm). In particular, BCT-Mn ceramics exhibited the best properties, with mechanical quality factor Q_m =1020, dielectric loss tanδ=0.2% and piezoelectric coefficient d₃₃ =190 pC/N. Furthermore, the planar electromechanical coupling factor k_p 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.