Revealing the mechanism of competing A-site doping ions in (K, Na)NbO₃-based ceramics

Although past studies have shown a competitive relationship between bismuth ion (Bi³⁺) and rare earth ions in potassium sodium niobate {(K, Na)NbO₃, KNN}-based ceramics, a comprehensive investigation of this competition has been relatively scarce. Herein, we conducted an in-depth exploration of this competition by substituting Bi³⁺ with praseodymium ions (Pr³⁺) in KNN-based ceramics possessing high piezoelectric properties. The substitution of Bi³⁺ with Pr³⁺ results in a decrease in the extent of multi-phase coexistence at room temperature, an increase in domain size and grain size, and the enhancement of ferroelectricity. However, it also leads to a deterioration in piezoelectricity. Through a combination of experimental findings and first-principles calculations, we analyzed the alterations in phase structure, ferroelectric domains, and electrical properties, attributing these changes to the competitive nature of Bi-O and Pr-O bonds with their distinct ionic/covalent characteristics. Consequently, this study not only unveils the underlying physical mechanism behind the competition between Bi³⁺ and Pr³⁺ ions in KNN-based piezoceramics but also presents a novel approach to tailor the phase transition temperature, thereby facilitating the overall performance improvement of KNN-based ceramics.