Potassium‐Sodium‐Niobate‐Based Thin Films: Lead Free for Micro‐Piezoelectrics

Abstract

Extensive research and great progress of (K,Na)NbO 3 (KNN)-based lead-free piezoelectric films have been driven by the current legislation and the requirement for sustainable development of society and environment in the applications of microelectromechanical systems. A comprehensive discussion of the recent achievement in KNN-based films is presented herein. First, the available synthetic techniques, chemical modification, the ferroelectric and piezoelectric properties of KNN-based films are reviewed, followed by an introduction of the crystal structures and electrical properties of KNN-based epitaxial films in comparison with the bulk ceramics. Finally, the applications of KNN-based films for the sensors, the energy harvesters, and energy storage devices are addressed, and current challenges and prospects for future work are discussed.

Giant Domain Wall Conductivity in Self‐Assembled BiFeO3 Nanocrystals

“…Self-assembled BiFeO 3 nanocrystals were grown on (100) SrTiO 3 :Nb (STO:Nb) single-crystal substrates using a sol-gel process (see Experimental Section), which is less-expensive and industrially scalable. [39,40] Figure 1a shows the topographic atomic force microscopy (AFM) images of the BiFeO 3 nanocrystals annealed at 800 °C. The lateral dimension of the crystal is ≈400-600 nm with an average height of ≈120 nm (Figure 1b).…”

Ferroelectric and dielectric properties of Ca2+-doped and Ca2+–Ti4+co-doped K0.5Na0.5NbO3thin films

“…Lead-free, nontoxic and biocompatible alternatives to PZT are especially important for in vivo biomedical applications 5 , and KNN has shown promising results in biocompatibility tests [6][7][8][9][10][11][12][13] . Materials in form of thin films are desired in many of these applications and there has been a considerable focus on development of KNN thin films [14][15][16] . To bring lead-free piezoelectric ceramics to the marked, economically viable large-scale industrial fabrication routes are required 2 .…”

Ferroelectric monoclinic phases in strained K0.70Na0.30NbO3 thin films promoting selective surface acoustic wave propagation

“…Nevertheless, first successful electromechanical characterization could be carried out yielding valuable information on the macroscopic piezoelectric K x Na 1-x NbO 3 films, when testing their ferro-and piezoelectric properties. [95][96][97] Their origin is not fully understood, yet. It might be attributed to the formation of oxygen vacancies originating from the volatilization of alkali metals at high temperatures during and after growth.…”