Effects and Mechanism of Combinational Chemical Agents on Solution‐Derived K_0.5Na_0.5NbO₃ Piezoelectric Thin Films

Abstract

Sodium potassium niobate (KNN) piezoelectric ceramic thin films were prepared by a chemical solution deposition method, in which the introduction of appropriately combinational organic stabilizing agents, including monoethanolamine (MEA), diethanolamine (DEA), and ethylenediaminetetraacetic acid (EDTA), dramatically suppressed the volatile loss of the alkali ions, improved the crystallinity, and promoted crystal orientation of the perovskite phase in the resulting KNN thin films. Theoretical analyses including ab initio calculation based on molecular model indicated that stronger binding structure could form comprising the alkali ions and the combinational EDTA-(DEA-MEA) chemical agents than the cases of using individual binding agents separately. Outstandingly large effective piezoelectric strain coefficient d 33 under the substrate clamping condition was achieved. The theoretical and experimental results provide the insight on the underlying interaction mechanism between the multiple stabilizing chemical agents and metal ions, and the guidance for establishing the methodology for producing high quality oxide thin films from chemical solutions with dedicatedly designed combinational stabilizing agents.

Effects of strontium doping on microstructure and functional properties of solution-derived potassium sodium niobate thin films

“…Modification of KNN solutions by stabilizing chemical agents, such as polyvinilpyrrolidone, ethanolamine, diethanolamine, ethylenediamine-tetra-acetic acid, was reported to have a positive influence on microstructure and overall functional properties of KNN thin film, including leakage current density [7,20,21]. In fact, chemical modification can suppress reactivity of niobium ethoxide in hydrolysis and polycondenzation reactions through shielding of the metal atoms by nonhydrolysable ligands, and even it can suppress the evaporation of potassium and sodium due to their better immobilization into organic matrix [7].…”

“…The films derived from the KNN sols with 10 mol% K and Na excess resulted in saturated hysteresis loops with 2P r ∼ 14 µC/cm 2 , 2E c ∼ 140 kV/cm and effective piezoelectric coefficient, d 33 of 46 pm/V measured by the scanning-probe microscope, SPM [6]. A large effective piezoelectric coefficient, d 33 of 83 pm/V was demonstrated for the KNN films derived from solutions in which the combination of ethylenediaminetetraacetic acid-diethanolamine-monoethanolamine stabilizing chemical agents was introduced to supress the loss of volatile alkali species and reduce the leakage current [7]. On the other hand, the shifting of T O−T phase transition to room temperature by Li-and Ta-modification of the KNN films followed by reduction of the leakage current density due to simultaneous co-doping with Mn allowed a significant improvement in ferroelectric properties (P r = 16.1 µC/cm 2 , E c = 22.2 kV/cm) and resulted in local piezoelectric coefficient, d 33 of 61 pm/V [8].…”

Outstanding Piezoelectric Performance in Lead‐Free 0.95(K,Na)(Sb,Nb)O3‐0.05(Bi,Na,K)ZrO3 Thick Films with Oriented Nanophase Coexistence

“…In the past few decades, lead zirconate titanate (PZT) thin films with excellent piezoelectric properties have dominated the commercial market of piezoelectric thin film devices. However, the high content of toxic lead composition in PZT raises environmental and human health concerns, thus increasing efforts are made to develop high performance lead‐free piezoelectric thin films as replacements . Among lead‐free piezoelectric ceramics, potassium sodium niobate, (K, Na)NbO 3 (KNN), is one of the most promising candidates with competitive piezoelectric properties over a broad temperature range, as obtained in KNN‐based bulk ceramics by constructing phase coexistence with complex chemical compositions .…”

Structure and High Performance of Lead-Free (K0.5Na0.5)NbO3 Piezoelectric Nanofibers with Surface-Induced Crystallization at Lowered Temperature

“…41 During the test, a unipolar AC signal of 5 V in amplitude at 1 kHz was applied to the nanofiber web with top Au electrode. 18,22,42 and comparable with un-doped PZT thin films. 41,43,44 Such an excellent piezoelectric performance makes the KNN nanofibers very attractive for electromechanical device applications.…”