LAUSR

Abstract Polycrystalline samples of composition (Na0.5Bi0.5)0.95−xBa0.05CaxTiO3 (x = 0.05, 0.075 and 0.1) were synthesized with the purpose of fabricating ceramics having morphotropic phase boundary by well known solid state reaction method. X-ray diffraction along with Rietveld-refinement showed a gradual change in crystal structure from rhombohedral to orthorhombic with increasing Ca doping in the host-matrix compound. The effect of Ca substitution on the electrical properties was studied by impedance spectroscopy in the temperature range 303 K 723 K. The dielectric properties of the synthesized ceramics were characterized by a strong temperature and frequency dependence. Complex impedance analysis distinguished the grain, grain boundary and electrode contribution and suggested that the systems are undergoing a polydispersive Non-Debye type relaxation. The equivalent circuit model was used to find a correlation between the response of real system and discrete electrical components. Combined study of imaginary part of electric impedance and modulus as a function of frequency was taken as additional evidence of electrical heterogeneous microstructure of the polycrystalline ceramics as explained by the Nyquist plots. The ac conductivity variation with frequency and temperature was investigated, which showed qualitative similarities as that of dielectric spectra. The dc conductivity was measured by extrapolating the conductivity spectra at different temperatures to the zero frequency values, from which thermal activation energies