Effect of excess Sr²⁺ on the microstructure and electrical properties of KSr₂Nb₅O₁₅ ceramics

KSr₂Nb₅O₁₅ (KSN) ferroelectric ceramics were prepared by the solid-state reaction method using rod-like KSN particles as raw material. The effect of excess Sr²⁺ on the microstructure and electrical properties of KSN-xSr (x=0, 2, 4, 6, 8 mol%) ceramics was investigated. The results indicated that all samples showed a single tetragonal tungsten bronze phase. Excessive Sr²⁺ diffuse into the A site of the KSN structure, compensating for the loss of A-site ions (Sr²⁺ and K⁺) of the raw materials, and alleviating the distortion of the lattice, which made the composition closer to the stoichiometric ratio of KSN. The Curie temperature shifted upward while the dielectric relaxor behavior was weakened as the excess Sr²⁺ content increased. In addition, dielectric tunability (T_u), ferroelectric, and piezoelectric properties of KSN ceramics were improved by increasing the excess Sr²⁺ content. The specimen with 6 mol% excess Sr²⁺ showed the optimum electrical properties, with T_u=18.48% at E=1 kV/mm, Pr=1.878 µC/cm², and d₃₃=40 pC/N. This work confirmed that A-site vacancies in the KSN raw materials can be compensated for by excess Sr²⁺.