Phase transformation and impedance spectroscopic study of Ba substituted Na0.5Bi0.5TiO3 ceramics

(Na0.5Bi0.5)(1-x)BaxTiO3 (x = 0.05, 0.1 and 0.15) ceramics abbreviated as (NBBT1, NBBT2 and NBBT3) are fabricated by conventional ceramic fabrication technique. The analysis of X-ray diffraction pattern of the prepared ceramic performed by Rietveld refinement indicate that crystal structure is rhombohedral for NBBT1, tetragonal for NBBT3 and a phase boundary occurs for NBBT2. Impedance spectroscopy has been employed to study the electrical properties of these ceramics in the frequency range of 10 Hz to 5 MHz and in a temperature range of 303 K-723 K. Frequency and temperature dependent electrical data is analyzed in the framework of conductivity, impedance and electric modulus formalisms. Conductivity spectrum obeys double power law for NBBT1, which is evidenced from two different dispersion regions. While for NBBT2 and NBBT3 only single power law is observed. Relaxation frequency for impedance is found to increase with temperature and obeys Arrhenius relationship with activation energy approximate to 0.764, 0.527 and 0.471 eV for NBBT1, NBBT2 and NBBT3 respectively. Variation of dielectric constant and tan delta with frequency at different temperatures was analyzed with the help of Maxwell-Wagner and Koop's phenomenogical theory. The presence of peaks in plots showing frequency dependence of tan delta for NBBT2 and NBBT3 indicates relaxor behavior of these compositions. (C) 2016 Elsevier B.V. All rights reserved.