Composition‐Driven Symmetry Manipulation and Correlation With Physical Properties of K 0.5 Na 0.5 NbO 3 –BiScO 3 Ferroelectric

A comprehensive investigation of composition‐driven symmetry modulation and the structure–property correlation in the lead‐free ferroelectric (1− x )K 0 . 5 Na 0 . 5 NbO 3 – x BiScO 3 (KNN‐ x BS) (0 ≤ x ≤ 0.05) system is discussed. Structural analysis using Rietveld refinement combined with Raman spectroscopy reveals a systematic evolution of the room‐temperature crystal symmetry from orthorhombic ( Amm 2, x = 0) to the coexistence of orthorhombic + monoclinic (0.005 ≤ x ≤ 0.010), to single‐phase monoclinic ( Pm , 0.015 ≤ x ≤ 0.020), and finally to coexistence of monoclinic + cubic ( x ≥ 0.030). Microstructural analysis demonstrates the systematic decrease of grain size with BiScO 3 substitution. Temperature‐dependent dielectric measurements demonstrated a progressive downward shift and broadening of the orthorhombic‐tetragonal ( T O – T ) and tetragonal‐cubic ( T T – C ) transitions with increasing x , with the T O – T transition shifting below room temperature for x ≥ 0.015. The composition x = 0.015 exhibits optimal functional response, with d 33 = 154 pC/N, ε r = 921 at T C , and 2 P r = 68 µC/cm 2 , within the monoclinic stability region. These findings elucidate the role of BiScO 3 ‐induced structural heterogeneity and phase coexistence in governing property enhancement in the modified KNN system. The study also provides insights into phase‐boundary engineering strategies in lead‐free perovskite ferroelectrics.