Investigation of MnO ₂ ‐doped (Ba, Ca)TiO ₃ lead‐free ceramics for high power piezoelectric applications

Abstract x % mol MnO 2 ‐doped Ba 0.925 Ca 0.075 TiO 3 ceramics (abbreviated as BCT‐Mn x , x =0‐1.5) were synthesized by conventional solid‐state reaction method. The effects of MnO 2 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 MnO 2 . 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 d 33 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 d 33 and Q m in MnO 2 ‐doped BCT ceramics make it a promising candidate for high power piezoelectric applications.