Rietveld refined structural, dielectric, and impedance properties of lead-free 1-x(K0.4Na0.6Nb0.96Sb0.04O3)-x(Bi0.5K0.5TiO3) (0.00 ≤ x ≤ 0.07) composites

A lead-free series of 1-x(K0.4Na0.6Nb0.96Sb0.04O3)-x(Bi-0.5 K0.5TiO3) (0.00 <= x <= 0.07) composites were prepared by the conventional solid-state reaction route. Rietveld's refined XRD pattern revealed phase transitions from orthorhombic (Amm2) to rhombohedral (R3m) and rhombohedral to tetragonal (P4mm) with x = 0.03 and 0.05 content of (Bi0.5K0.5TiO3). SEM images reveal that the microstructure consists of small, randomly oriented, well-inter-linked, and non-uniform-shaped grains. Dielectric study indicates that Curie temperature (T-C) decreases from 340 to 160 degrees C as the BKT content increases from x = 0.00 to 0.07 and the first transition temperature shifts below room temperature. The complex modulus plots exhibited two semicircles, confirming the ceramics' presence of bulk grain and grain boundary. The impedance and modulus plots confirm the presence of a non-Debye type of relaxation in the ceramics. The ac conductivity increases with a rise in the temperature, confirming negative temperature coefficient resistance (NTCR) behavior. Therefore, conductivity may increase due to the charge carrier hopping rate or the oxygen vacancies (V ''(O)).