Ultrahigh Performance in Lead-Free Piezoceramics Utilizing a Relaxor Slush Polar State with Multiphase Coexistence

Abstract

Owing to growing environmental concerns, the development of lead-free piezoelectrics with comparable performance to the benchmark Pb­(Zr,Ti)­O3 (PZT) becomes of great urgency. However, a further enhancement of lead-free piezoelectrics based on existing strategies has reached a bottleneck. Here we achieve a slush polar state with multiphase coexistence in lead-free potassium–sodium niobate (KNN) piezoceramics, which shows a novel relaxor behavior, i.e., frequency dispersion at the transition between different ferroelectric phases. It is very different from the conventional relaxor behavior which occurs at the paraelectric–ferroelectric phase transition. We obtain an ultrahigh piezoelectric coefficient (d 33) of 650 ± 20 pC/N, the largest value of nontextured KNN-based ceramics, outperforming that of the commercialized PZT-5H. Atomic-resolution polarization mapping by Z-contrast imaging from different orientations reveals the entire material to comprise polar nanoregions with multiphase coexistence, which is again very different from conventional ferroelectric relaxors which have polar domains within a nonpolar matrix. Theoretical simulations validate the significantly decreased energy barrier and polarization anisotropy, which is facilitated by the high-density domain boundaries with easy polarization rotation bridging the multiphase-coexisting nanodomains. This work demonstrates a new strategy for designing lead-free piezoelectrics with further enhanced performance, which should also be applicable to other functional materials requiring a slush (flexible) state with respect to external stimulus.

Reduced degree of phase coexistence in KNN-Based ceramics by competing additives

“…K2CO3 (99%), Na2CO3 (99.8%), Nb2O5 (99.5%), Bi2O3 (99.999%), BaCO3 (99.9%), Fe2O3 (99%), Ag2O (99.7%) and ZrO2 (99.5%) (Sinopharm Chemical Reagent Co., Ltd, China) were selected as raw materials. 0.2wt% Fe2O3 was doped to promote the sinterability of KNN-based ceramics [7]. All raw materials were dried at 180 oC for 3 h due to the hygroscopicity.…”

“…Inspired by this, Wu et al proposed a new way to construct the multi-phase coexistence by simultaneously adjusting TO-T and rhombohedral-orthorhombic phase transition temperature (TR-O) to the room temperature after ten years, resulting in the continuous increase in piezoelectric coefficient d33 [1,[7][8][9][10][11][12]. Currently, d33 values of state-of-the-art non-textured KNN-based ceramics are as high as 400-650 pC/N, comparable to those of commercial soft PZT-based ceramics [1,7,11,12].…”

Ultrahigh Discharge Efficiency and High Energy Density in Sandwich Structure K0.5Na0.5NbO3 Nanofibers/Poly(vinylidene fluoride) Composites

“…The excellent performance of KNN ceramics is comparable to Pb(Zr 0.5 Ti 0.5 )O 3 (PZT) ceramics. [ 43–47 ] Among the lead‐free piezoelectric materials, it is regarded as the extremely potential candidate to substitute for PZT ceramics. However, the research on KNN/PVDF composites, especially 1D KNN nanofibers (KNN‐nfs), is a new type of polymer energy storage material, and there are few reports on the research in the field of energy storage.…”

Second‐order‐transition like characteristic contributes to strain temperature stability in (K, Na)NbO3‐based materials

“…Piezoelectric materials are indispensable components in our industrial production . Due to Pb toxicity in commercial lead‐based piezo‐materials, lead‐free piezoelectrics have received much attention in recent years . Potassium‐sodium niobate [(K, Na)NbO 3 , KNN] is one of the most promising lead‐free candidates because of its high Curie temperature ( T C =415 °C) and relatively good piezoelectric constant ( d 33 ) .…”

“…[1][2][3][4][5] Due to Pb toxicity in commercial leadbased piezo-materials, lead-free piezoelectrics have received much attention in recent years. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] Potassium-sodium niobate [(K, Na)NbO 3 , KNN] is one of the most promising lead-free candidates because of its high Curie temperature (T C =415 °C) and relatively good piezoelectric constant (d 33 ). 8,[25][26][27][28] For small signal applications, such as sensors and microphones, d 33 is a research emphasis.…”