Ultra-high piezoelectric performance by rational tuning of heterovalent-ion doping in lead-free piezoelectric ceramics

The vision of “lead-free” instead of “lead” is growing as people pay more attention to environmental problems, especially since performance improvement of lead-free piezoelectric materials is imminent. The introduction of local heterogeneity, relaxor behavior, and nanodomain engineering based on heterovalent-ions has been proved to be highly effective for further increasing of performance of piezoelectric materials. However, how the doping level will work towards improving the piezoelectric performance, especially the lead-free piezoelectrics is an open question. In this work, we have assembled (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 ceramics based on the traditional phase-structure construction strategy and used microscale heterovalent-ion Al element doping to regulate its piezoelectric properties. The optimization of piezoelectric properties, on the one hand, comes from large lattice distortion caused by appropriate Al doping, leading to high asymmetry and enhancement of the displacement of B−site ions. On the other hand, the behavior of a ceramic with a low defect concentration and an N-type conductivity mechanism is guided by its defect chemistry. The defect configuration analysis explains in detail the process of Al3+ ions entering A-sites and B-sites in turn with change in the doping concentration, that is, from donor doping to acceptor doping, and the influence of the change in defect concentration caused by this process on piezoelectric properties. When the doping level of Al3+ ions is 0.25 mol%, it is exciting to find that the piezoelectric performance is significantly high (piezoelectric coefficient d33 = 638 pC/N, electromechanical coupling factor kp = 54%). The interpretation of heterovalent-ion doping in this work is different from the strategy for traditional high-performance piezoelectric materials. This discovery facilitates a new mechanism of doping for improving piezoelectricity, which will help to further improve the piezoelectric performance of different piezoelectric materials.