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

Abstract

Lead-free (K,Na)NbO 3 (KNN) piezoelectric films were fabricated on Nb:SrTiO 3 substrates by sol-gel process, and the influence of thermal processing details on the microstructure and ferroelectric property was investigated. Experimental results confirmed the different appearance of polycrystalline growth and epitaxial growth modes during the crystallization of KNN thin films. These two growth modes occurred under different thermal conditions within the narrow pyrolysis temperature scope ranging from 400°C to 500°C, respectively. By considering these findings, an optimizing combination between pyrolysis and annealing procedure was thought to be crucially important to obtain high-performance KNN films with excellent crystallization state.

Determination of crystallographic orientation of lead-free piezoelectric (K,Na)NbO3 epitaxial thin films grown on SrTiO3 (100) surfaces

“…5(b). However, a previous study revealed an accompanying growth mode of the [101] preferred orientation in [110]-oriented films 16. For this [101] growth, the [101] polarization dipole is parallel to the film normal direction (also the test direction).…”

“…11 However, more detailed studies are needed to investigate the precise crystallographic structure of KNN films on cubic substrates because of the lattice parameter differences existing between KNN and PZT systems. 14, 15 We fabricated KNN-based films by sol-gel processing, whose details can be found elsewhere, 8,16 The sol solution was prepared from sodium ethoxide [NaOC 2 H 5 ] (>99%), potassium ethoxide [KOC 2 H 5 ] (>98%), niobium pentaethoxide [Nb(OC 2 H 5 ) 5 ] (>99.999%), and manganese acetate [Mn(CH 3 COO) 2 ] (>98%), which was dissolved in 2-methoxyethanol (>99.0%) with acetic acid (>99.5%), acetylacetone (>99.0%), and formamide (>99.0%) as stabilizer, chelating agent, and drying controller, respectively. The compositions of the solution were adjusted to (K 0.5 Na 0.5 )NbO 3 with 10% alkali-metals excess and 2% Mn-doping to reduce leakage current without changing phase structure.…”

Influence of Yttrium Dopant on the Structure and Electrical Conductivity of Potassium Sodium Niobate Thin Films

“…This incorporation would create ionic compensation between Nb 5+ and Y 3+ at the B-site and reduce the interaction of octahedron molecules (Nb 5+ and O 2-) as a result. Due to weak octahedron interaction, the oxygen rapidly vaporizes and induces the oxygen vacancies in the KNN lattice 24 . Following that, the oxygen vacancies promote the localized defects in KNN lattices which cause the conductivity to be reduced remarkably.…”

Growth and physical properties of highly oriented La-doped (K,Na)NbO3 ferroelectric thin films

“…As can be observed, the KNN films obtained with low excess amount of alkaline metals, 0 mol% (50/50) and 10 mol% (60/60), show a higher degree of misorientation with the presence of other reflexions different to those of {100} orientation associated to the formation of the secondary phase. It is known that the pyrolysis temperature is a critical processing condition parameter for preferential orientation [13,21]. In our study, all the films were prepared under the same pyrolysis conditions and only the excess amount of Na and K was changed.…”

“…Although textured films can been obtained using SrTiO 3 (STO) substrates [13], the main problems concerning KNN-based thin films are the low stability of the precursor solutions, the low control of stoichiometry and the difficulty in achieving epitaxial films.…”