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

Abstract

It is challenging to achieve highly tunable multifunctional 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 electrostrictive 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 ∼ 539 pC/N) and the temperature-insensitive strain (the unipolar strain varies less than 8% at 27–120 °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 m4/C2), 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.

Evolution Characteristics of Electric Field-Related Properties in Polymorphic Piezoceramics with Temperature-Impelled Phase Transition

“…The obvious domain extension behavior before T phase should contribute to this phenomenon. The domain extension under a high electric field can contribute a higher electrostrictive strain than the strain induced by the pure electrostrictive effect with only ions shifting around T-C (here T and C phases are included) [29,30]. On the other hand, it can be seen that Q 33 gradually becomes a constant when the electric field is elevated to a high value.…”

Simultaneously enhanced energy storage performance and luminance resistance in (K 0.5Na 0.5)NbO 3-based ceramics via synergistic optimization strategy

“…In the case of the 85KNN-15BZT-1La ceramics, T m obtained from the temperature-dependent ε curve at 1 MHz in Fig. 2 T m , γ, and C are the temperature corresponding to ε max , the diffusion factor, and the Curie-like constant, respectively [25,26].…”

Multiscale Structure Engineering for High-Performance Pb-Free Piezoceramics

“…Considering the two ferroelectric–ferroelectric phase transitions in KNN ceramics, our group attempted to simultaneously shift T O–T and T R–O to room temperature for constructing a new phase boundary (NPB) that differs from previous ones constructed by shifting T O–T or T R–O alone. ,, Thus, seeking adequate chemical dopants is quite challenging. Through the combined considerations from ion radius, valence, and electronegativity, the database of potential dopants was obtained (Figure c,d). ,, In particular, antimony (Sb), bismuth (Bi), zirconium (Zr), and hafnium (Hf) are key elements for constructing the NPB. ,, Doping Sb can effectively increase T R–O and reduce T O–T to some degree . Doping Bi also effectively decreases T O–T , while Zr and Hf neutralize the charges caused by doping Bi .…”

“…These dopants cause the isovalent and/or heterovalent ionic substitutions at both A- and B-sites, preventing the formation of long-range ferroelectric ordering and promoting the formation of short-range polar regions (e.g., polar nanoregions, PNRs) . In other words, these dopants not only shift the phase transition temperatures but also gradually enhance the degree of dielectric dispersion, resulting in the formation of a diffused multiphase coexistence (Figure f). ,, Compared to the sharpened (or fast) phase transitions of unmodified PPB (e.g., orthorhombic–tetragonal phase transition of pristine KNN ceramics), the diffused multiphase coexistence exists over a relatively wide temperature range and consequently promotes the temperature stability (Figure f) . Since the NPB is still affected by the temperature, the temperature stability around the NPB cannot completely match that around the MPB that is independent of temperature (Figure ).…”