Composition‐Driven Symmetry Manipulation and Correlation With Physical Properties of K 0.5 Na 0.5 NbO 3
Abhisikta Sahu, Satyaranjan Sahoo, Anupam Mishra, Priya Choudhary, Sudhindra Rayaprol, Akhilesh Kumar Singh, Dhiren K. Pradhan, Shalini Kumari, Md. Mijanur Rahaman, Reji Thomas, Banarji Behera, Ashok Kumar, Philip D. Rack, Dillip K. PradhanABSTRACT
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.