Investigation of MnO2-doped (Ba, Ca)TiO3 lead-free ceramics for high power piezoelectric applications
x% mol MnO2-doped Ba0.925Ca0.075TiO3 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 Ei was determined from the asymmetrical polarization hysteresis loops and found to increase with the doping concentration of MnO2. High mechanical quality factors (Qm>1200) and low dielectric loss (tanδ3 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 Qm, being on the order of 1000. The high d33 and Qm in MnO2-doped BCT ceramics make it a promising candidate for high power piezoelectric applications.