Alternating Spin-Coating Sol–Gel Synthetic Route for Highly (100)-Textured Potassium Sodium Niobate Films

Abstract

This study introduces a novel sol−gel synthesis route that combines the metal alkoxide and nonalkoxide methods to synthesize highly preferentially oriented potassium sodium niobate (KNN) films. In this approach, C 10 H 25 NbO 5 and Nb 2 O 5 are used as niobium sources to synthesize KNN sols, which are then alternately spin-coated to form the desired KNN film (referred to as e-KNN/o-KNN). Pure C 10 H 25 NbO 5 source KNN film (e-KNN) and pure Nb 2 O 5 source KNN film (o-KNN) are also synthesized as control samples. As expected, alternating spincoating facilitates the enhancement of (h00)-preferred orientation and crystallinity, and both were superior to the KNN film with alternating e-KNN and o-KNN layers compared with the two pure KNN films. Interestingly, variations in annealing temperature do not affect the crystalline characteristics of these three types of KNN films, indicating that the synthesis route plays a predominant role in determining the microstructural characteristics. Furthermore, the dielectric response and optical properties of KNN films can also be precisely tailored through the synthesis route. For instance, using Nb 2 O 5 as a niobium source can significantly enhance the dielectric constant of KNN films, whereas substituting C 10 H 25 NbO 5 for Nb 2 O 5 can effectively accelerate the dielectric polarization speed of KNN films, thereby reducing their high-frequency dielectric losses. This research provides new insights and significant guidance for tailoring the sol−gel synthesis, microstructural characteristics, and performance of KNN films.