Low-temperature dielectric relaxation associated with NbO₆ octahedron distortion in antimony modified potassium sodium niobate ceramics

Although the antimony (Sb) has been widely used to modify potassium sodium niobate (KNN) ceramics for tailoring the phase structure and performance, the role of Sb still remains insufficiently understood, consequently hindering the understanding of the physical origin of high-performance KNN-based ceramics. Here, we combine the experiments and first-principles calculations to deeply reveal the effects of Sb on KNN ceramics. Our results reveal a re-entrant-like relaxation behavior near the rhombohedral-orthorhombic (R-O) phase transition at the low content of Sb, which transforms into a canonical one at higher content of Sb. First-principles calculations show a significantly decreased difference in the bond length of six B-O bonds of NbO₆ octahedral in Sb-modified KNN ceramics compared to pristine KNN ceramics, responsible for the low-temperature re-entrant-like dielectric relaxation. Furthermore, the addition of Sb would soften the B-O repulsion and gradually break the long-range ferroelectric ordering, resulting in the occurrence of nanoscale domains and enhanced local heterogeneity. Finally, we find that the optimized piezoelectric properties are the trade-off between the long-range ferroelectric ordering and the local heterogeneity. Therefore, this work not only deeply reveals the effects of Sb on KNN ceramics from multi-scale perspectives but also helps the future composition design for achieving high piezoelectricity.