Local distortion determination of the (1 − x) (K_0.5Na_0.5)NbO₃ − x (Ba_0.8Sr_0.2)TiO₃ system and their influence on the electrical properties

The composition of (1 − x) (K_0.5Na_0.5)NbO₃ − x (Ba_0.8Sr_0.2)TiO₃ and termed as (1 − x) KNN – x BST for x = 0, 0.1 and x = 0.2 were successfully synthesized using a combination of solid-state reaction and co-precipitation oxalate methods. Structure and local distortion determination were carried out using X-Ray diffraction (XRD), and X-ray absorption spectroscopy (XAS) Ti K-edge data. The XRD was utilized to investigate the phase present in the sample and crystal structure determination through Rietveld refinements, while local distortion due to the defects were studied by XANES and EXAFS at the Ti K-edge. XRD analysis at room temperature concluded that both KNN–BST samples exhibit tetragonal structure compared to orthorhombic for KNN, while EXAFS analysis using Artemis software revealed the oxygen octahedral distortion and distance of Ti_Nb^′ to its surroundings of A site ions (K, Na. Ba_K^•, Sr_Na^•) and B site ions (Nb⁵⁺). Electrical characterizations of dielectric properties and conductivity were investigated to elucidate the changes in local distortion. Conductivity measurements at various temperatures showed an alteration of curves slope from positive at low temperature region become negative at high temperature. The temperature inflection of ln σ vs 1/T curve, was shift to higher temperature for doped samples, T ≈ 160 °C for KNN and T ≈ 232–260 °C for KNN–BST. The characterization of dielectric properties exhibited a broader peak which is a typical relaxor characteristic and was thought to be related to the distortion of oxygen octahedral arrangement surrounding the B sites in the ABO₃ structure.