Feasible Way to Achieve Multifunctional (K, Na)NbO3-Based Ceramics: Controlling Long-Range Ferroelectric Ordering

It is challenging to achieve highly tunable multi-functional properties in one piezoelectric ceramic system through a simple method due to the complicated relationship between the microscopic structure and macroscopic property. Here, multifunctional potassium sodium niobate [(K, Na)NbO3 (KNN)]-based lead-free piezoceramics with tunable piezoelectric and electro-strictive properties are achieved by controlling the long-range ferroelectric ordering (LRFO) through antimony (Sb) doping. At a low Sb doping, the slightly distorted NbO6 octahedron and the softened B-O repulsion well maintain the LRFO and induce plenty of nanoscale domains coexisting with a few polar nanoregions (PNRs). Thereby, the diffused rhombohedral-orthorhombic-tetragonal (R-O-T) multiphase coexistence with distinct dielectric jumping is constructed near room temperature, by which the nearly 2-fold increase in the piezoelectric coefficient (d(33) similar to 539 pC/N) and the temperature-insensitive strain (the unipolar strain varies less than 8% at 27-120 degrees C) are obtained. At a high Sb doping, the LRFO is significantly destroyed, leading to predominant PNRs. Thus, a typical relaxor is obtained at the ferroelectric-paraelectric phase transition near room temperature, in which a large electrostrictive coefficient (Q(33) = 0.035 m(4)/C-2), independent of the electric field and temperature, is obtained and comparable to that of lead-based materials. Therefore, our results prove that controlling the LRFO is a feasible way to achieve high-performance multifunctional KNN-based ceramics and is beneficial to the future composition design for KNN-based ceramics.