Rietveld refinement, impedance spectroscopy and magnetic properties of Bi_(0.8)Sr_(0.2)FeO_3 substituted Na_(0.5)Bi_(0.5)TiO_3 ceramics

摘要

We herein presented the investigation on the structural, electrical and magnetic properties of (1 -x)(Na_(0.5)Bi_(0.5)TiO_3)-x(Bi_(0.8)Sr_(0.2)FeO_3) polycrystalline ceramic samples, with x=0.1, 0.3, 0.5 and 0.7. These samples were prepared by conventional solid state reaction method and the crystalline phase of prepared ceramics was identified with the help of X-ray diffraction pattern. Rietveld analysis of the obtained XRD data confirmed that all the synthesized samples adopt the rhombohedral crystal structure with R3c space group. Impedance spectroscopic measurements were performed on all the compositions in the frequency range 10 Hz-5 MHz to probe the electrical microstructure of polycrystalline (1-x)(Na_(0.5)Bi_(0.5)TiO_3)-x(Bi_(0.8)Sr_(0.2)FeO_3) ceramics, which changes significantly as a function of x (content of BSFO). A significant increase in dielectric constant has been observed with increase in BSFO concentration, which was attributed to enhancement of oxygen vacancies. Detailed study of impedance complex plane plots revealed the presence of non-Debye type relaxation for all the prepared systems and enabled us to separate the contribution from grains and grain boundaries. Equivalent circuit model (R_gCPE_g)(R_(gb)CPE_(gb))(R_eCPE_e) was employed to explain the impedance data for all the prepared samples. The activation energies obtained from electric modulus as well as dc conductivity increase with increase in BSFO content which approaches the value 1 eV and indicates an Arrehenius type thermally activated process. Remnant magnetization (M_r) and coercive field (H_c) are found to be increase with BSFO concentration.