Investigation of MnO2‐doped (Ba,Ca)TiO3 lead‐free ceramics for high power piezoelectric applications

x% mol MnO₂‐doped Ba_0.925Ca_0.075TiO₃ ceramics (abbreviated as BCT‐Mnx, x=0‐1.5) were synthesized by conventional solid‐state reaction method. The effects of MnO₂ addition and (Ba+Ca)/Ti mole ratio (A/B ratio) on the microstructure and electrical properties of the ceramics were investigated. The internal bias filed E_i was determined from the asymmetrical polarization hysteresis loops and found to increase with the doping concentration of MnO₂. High mechanical quality factors (Q_m>1200) and low dielectric loss (tanδ<0.5%) were found in the BCT‐Mn0.75 and BCT‐Mn1.0 ceramics with E_i>3 kV/cm, meanwhile, the piezoelectric and electromechanical properties were found to decrease compared with the pure BCT, exhibiting a typical characteristic of “hard” behavior. Of particular interest is that the microstructure of BCT‐Mn0.75 ceramics could be controlled by changing the A/B ratio, where enhanced piezoelectric coefficient d₃₃ on the order of 190 pC/N was obtained in the BCT‐Mn0.75 ceramics with A/B=1.01 due to its fine‐grained microstructure, with yet high Q_m, being on the order of 1000. The high d₃₃ and Q_m in MnO₂‐doped BCT ceramics make it a promising candidate for high power piezoelectric applications.