Piezoelectric and ferroelectric property in Mn-doped 0.69BiFeO3–0.04Bi(Zn1/2Ti1/2)O3–0.27BaTiO3 lead-free piezoceramics

In this article, rhombohedral 0.69BiFeO3–0.04Bi(Zn1/2Ti1/2)O3–0.27BaTiO3 (BF69–BZT4–BT27) lead-free piezoceramics were studied for the sake of obtaining high Curie point and piezoresponse. In compositional engineering approach, A-site vacancies with various concentrations were introduced in advance into ferroelectric ceramics by using low purities of raw oxides and doping MnO2. In contrast to lossy BF–BT ceramics, very low dielectric loss tanδ ~ 0.03 was obtained in the BF69–BZT4–BT27 ceramics through adding BZT third member to stabilize perovskite phase and doping MnO2 to reduce oxygen vacancies with a refined solid state reaction electroceramic processing. A good combination of ferroelectric and piezoelectric property was obtained in the 0.17 wt% MnO2-doped BF69–BZT4–BT27 coarse-grained ceramics with remanent polarization of Pr = 32.3 μC/cm2, piezoelectric constant of d33 = 145 pC/N, thickness electromechanical coupling coefficient of kt = 0.41 and Curie temperature of TC = 510 °C. The intrinsic piezoelectric response was observed in correlation with ferroelectric polarization switching power described by dielectric constant, which is affected by some extrinsic factors such as point defects, microstructure grain size, and residual internal stresses. Excellent thermal aging stability of piezoelectric constant d33 were also experimentally demonstrated and argued resulting from the higher TC and no ferroelectric–ferroelectric structural phase transition below TC of BF–BZT–BT system.