High Strain in (K,Na)NbO₃-Based Lead-Free Piezoelectric Fibers

Abstract

Until now, lead zirconate titanate (PZT)-based ceramics are the most widely used in piezoelectric devices. However, the use of lead is being avoided due to its toxicity and environmental risks. Indeed, the attention has been moved to lead-free ceramics, especially on potassium sodium niobate (KNN)-based materials, due to growing environmental concerns. These materials are technologically interesting. For applications such as actuators, an electromechanical coupling providing high strain with high force, e.g, fuel injection, ultrasonic motor, etc., is required, Moreover, in the current context, the new technologies evolve toward the miniaturization of the conventional electronic devices. Herein, we have developed microfiber ceramics of KNN-based composition, which yield a high strain value with S max as high as 0.17% at 3 kV mm −1 . According to our results, this phenomenon can be explained by an extrinsic effect that favors the internal relaxation of the system. To reach this breakthrough, a sintering mechanism has been established, which allows for correlating the extrinsic factors of the system with electromechanical properties of the ceramic fibers. We believe that the general strategy and design principles described in this study will open new avenues in developing of (K,Na)NbO 3 -based lead-free piezoelectric fibers with enhanced properties for high-precision sensor and actuator applications.

Exploring optoelectronic properties and mechanisms of layered ferroelectric K4Nb6O17 nanocrystalline films and nanolaminas

“…It was noteworthy that, KN was easily formed as a secondary phase caused by the volatilization of alkali metal ions, when preparing the K 0.5 Na 0.5 NbO 3 film in our previous study 33 . Moreover, this phenomenon also frequently occurs in the preparation of ferroelectric KNbO 3 and K x Na 1− x NbO 3 based ceramic and film 34–36 . KN has an orthorhombic structure with space group P 2 1 nb , and its single crystal was reported to show weak ferroelectricity 13, 37–39 .…”

Losses in ferroelectric materials

“…Up to now, perovskite-type lead free ferroelectrics were believed to be promising materials to replace PZTs due to their relatively high dielectric and piezoelectric properties, in which potassium sodium niobate (KNN) and bismuth sodium titanate (Na 1/2 Bi 1/2 TiO 3 , NBT for short) based materials are two lead-free piezoelectric ceramics received a lot of attentions [274–277]. …”

Hydrothermal crystal growth, piezoelectricity, and triboluminescence of KNaNbOF5

“…This phenomenon can be observed with the naked eye in a dark room with pupils fully dilated. It is interesting to note, however, that triboluminescence can also be observed in centrosymmetric (CS) materials such as doped fluorites [7]. TL is therefore a phenomenon with several possible origins that are not completely understood, where any one explanation cannot be applied to all triboluminescing materials.…”

“…While the electromechanical responses of KNN based materials do not yet meet those of PZT, properties have been enhanced through doping, sintering processes, and domain engineering [7]. Strong TL in the noncentrosymmetric (NCS) polymorph of KNaNbOF 5 , visible with the naked eye under normal lighting conditions, was observed as blue sparks when this phase was first grown.…”