The composition of (1 − x) (K0.5Na0.5)NbO3 − x (Ba0.8Sr0.2)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 TiNb′ to its surroundings of A site ions (K, Na. BaK•, SrNa•) 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.
|Number of pages
|Journal of Materials Science: Materials in Electronics
|Published - 1 Jan 2018