Sharpening polycrystalline phase boundary for potassium sodium niobate ceramics with MnF2 modification.

The influence of anion on structure and performance is unclear in potassium sodium niobate ((K,Na)NbO3; KNN)‐based ceramics, while cation doping has been widely researched. Here, the phase structure and electrical properties are explored in MnF2‐doped KNN ceramics. Significantly, sharp rhombohedral–orthorhombic (R–O) and orthorhombic–tetragonal (O–T) phase boundary as well as reduced diffusion degree is exhibited in the ceramics along with little changed phase transition temperatures due to the optimized F− content at O site, which is different from that of cation replacement for A and B sites. Notably, the domain wall motion is facilitated due to the increased A vacancy and decreased O vacancy along with strengthened polarity, originating from the higher valence state and electronegativity of F− with respect to O2−. And then, enhanced ferroelectricity is realized via MnF2 modification, the piezoelectricity is elevated in turn. This work presents a new idea of anion doping for controlling structure and properties in perovskite materials. [ABSTRACT FROM AUTHOR]