Effect of bismuth and titanium ions on structural, optical and electrical properties of lead-free K 0.5 Na 0.5 NbO 3 ceramics

([K 0.5 Na 0.5 ] 1 −x Bi x [Nb 1 − x Ti x ])O 3 - KNN-100 x BT) ceramics with x = 0.00 to 0.08 were synthesized using the conventional sintering technique. X-ray diffraction studies confirmed the stable perovskite phase formation in all compositions without any sign of a secondary phase. No composition-driven structural phase transition was observed in the chosen composition range. Room-temperature Raman studies were performed on all the samples to identify the local lattice dynamics and crystal structure. Microstructure analysis showed dense features for higher concentration of dopants. X-ray photon spectroscopy confirmed the substitution of Bi 3+ and Ti 4+ ions in the host KNN lattice. The combined effects of bismuth and titanium substitution lead to a downward shift in the orthorhombic–tetragonal ( T O−T ) phase transition temperature and Curie temperature ( T c ). An optimal dielectric constant (ε r ) of 1700, spontaneous polarization ( P s) of 25 µC/cm 2 , piezoelectric strain of 0.24% and d 33 of 235 pC/N were obtained for the KNN-08BT. The improved properties of KNN-08BT make it a promising candidate for piezoelectric transducer applications.