Investigations of the mechanism of enhanced relaxor ferroelectricity of （K，Na）_1－2x Sr _x NbO₃ lead-free piezoelectric ceramics

（K，Na）_1-2x Sr _x NbO₃ （KNSN） ceramics were synthesized via solid-state sintering method， building upon the preparation of KNSN powders by the conventional solid-state reaction method. The regulatory mechanisms of Sr²⁺ doping on crystal structural evolution， dielectric relaxation behavior， and ferroelectric properties were systematically investigated. The phase structure， surface morphology， dielectric properties， and ferroelectric performance of the ceramics were characterized using X-ray diffraction （XRD）， scanning electron microscopy （SEM）， precision impedance analysis， and ferroelectric testing systems， respectively. Experimental results demonstrated that， the KNSN ceramics exhibited the enhanced structural symmetry， improved densification， and strengthened dielectric relaxation with increasing Sr²⁺ doping content. The modulation of relaxor ferroelectric behavior in sodium potassium niobate-based lead-free piezoelectric ceramics was revealed through Sr²⁺ doping and clarifying the underlying mechanisms systematically， providing both theoretical and experimental support for the design of high-performance lead-free relaxor ferroelectrics.