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.