Multi-scale understanding the effect of K/na ratio on electrical properties of high-performance KNN-based ceramics

Although certain efforts were paid to the effect of K/Na ratio on the phase structure and piezoelectric properties of potassium sodium niobate {(K, Na)NbO3, KNN}-based ceramics, insufficient attention was given to the local structure and ferroelectric domains, hindering the further understanding of physical mechanisms. Herein, we studied the effect of the K/Na ratio on KNN-based ceramics with multi-phase coexistence from multi-scale structure. High Na+ content leads to local stress heterogeneity and retains large ferroelectric domains, while high K+ content rotates the NbO6 octahedron and results in local polarity heterogeneity and distinct dielectric relaxational behavior, consequently fragmenting ferroelectric domains. The improved piezoelectricity is obtained at the equal K/Na ratio and originates from the balanced local polarity and stress heterogeneities. Therefore, an appropriate K/Na ratio should be fully considered when designing compositions with the purpose of improving performance of KNN-based ceramics in the future.