Reaction Mechanisms of Ethylenediaminetetraacetic Acid and Diethanolamine in the Precursor Solution for Producing (K, Na)NbO₃ Thin Films with Outstanding Piezoelectric Properties

Abstract

An understanding of the reaction mechanisms of ethylenediaminetetraacetic acid (EDTA) and diethanolamine (DEA) for producing solution-derived (K, Na)NbO3 (KNN) thin films with outstanding piezoelectric properties and low leakage current is developed. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance spectroscopy (NMR) were used to analyze the interactions among EDTA, DEA, and metal cations in both precursor solutions and amorphous films. XPS analyses showed that the oxidation states of potassium, niobium, and oxygen in KNN amorphous film were enhanced with addition of EDTA and DEA in the precursor solution, which shifted closer to the oxidation states in the perovskite phase of the resulting KNN oxide film. FTIR analyses indicated that EDTA and DEA formed dative bonds with the nonhydrated potassium and sodium acetate after pyrolysis process at 330 °C while NMR analyses showed that such interactions could have occurred in the precursor solution. NMR analyses also indicated that DEA could have chelated niobium precursor. It is proposed that EDTA and DEA acted as a “bridge” that linked the metal precursors in the solution, which is critical to suppressing the volatilization of the metal cations, for achieving the reported outstanding electrical properties of the resulting KNN films.

Potassium–Sodium Niobate‐Based Lead‐Free Piezoelectric Ceramic Coatings by Thermal Spray Process

“…The high piezoelectricity of the KNN‐based systems further enables the potential of replacing lead‐based piezoceramics, as stated in recent reviews . Significant progress has been made in KNN‐based piezoelectric thin films fabricated by solution deposition method . However, no progress has been made for forming piezoelectric ceramic coatings by thermal spray process as a method with the desirable high productivity, increased thickness range, and capability of large area coating for many industry applications.…”

Effects and Mechanism of Combinational Chemical Agents on Solution‐Derived K0.5Na0.5NbO3 Piezoelectric Thin Films

“…The positive alkali ions, Na + and K + in KNN could then be bonded to the above complex chemical structure, through the lone pair electrons of oxygen and nitrogen, and be immobilized in the chemical agents' networks . Thus, these large networks could suppress the volatile loss of alkali ions in KNN precursor even at elevated temperature until these chemical agents were fully decomposed .…”

“…Only compensating potassium and sodium loss by adding excess compositions in the precursors cannot effectively maintain or control the stoichiometric composition of KNN films. It was reported that for the solution‐derived KNN films, introducing selected chemical agents in the precursor solutions could suppress the loss of potassium and sodium in the resulting thin films . So far, many chemicals have been used as stabilizing chemical agents for producing KNN thin films, including acetylacetone (AcAc), polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), diethanolamine (DEA), and ethylenediaminetetraacetic acid (EDTA) .…”

Effect of Pyrolysis Temperature on Sol–Gel Synthesis of Lead‐free Piezoelectric (K,Na)NbO3 Films on Nb:SrTiO3 Substrates

“…For example, the long‐standing volatilization problem of alkali metal elements was regarded as the main source of the performance deterioration and poor‐stability in KNN system, which could be suppressed by adding excessive raw materials . And also, Mn‐doping as well as adding organic agents, were treated as an effective way to reduce the leakage current . On the basis of elementary exploration of preparation technology, some deeper attempts associated with intrinsic mechanism and domain configuration were made on single‐crystalline substrates, on which epitaxial thin films were obtained .…”