Dielectric and impedance spectroscopy of Sr(Bi0.5Nb0.5)O3 ceramics

A lead free polycrystalline material Sr(Bi0.5Nb0.5)O3 was prepared using a high-temperature solid-state reaction technique. Preliminary X-rays diffraction studies exhibit the formation of a single-phase compound in the orthorhombic crystal system. The study of microstructure of gold-coated pellet by scanning electron microscopy (SEM) shows well-defined and homogeneous distribution of grains on the surface of the sample. Detailed studies of dielectric parameters (i.e., εr and tan δ) of the compound as a function of temperature at selected frequencies reveal that the values of these parameters are almost independent of temperature. Studies of impedance and related parameters exhibit that these electrical properties of the material are strongly dependent on temperature, and bear a good correlation with the microstructure of the material. The decrease in value of bulk resistance on increasing temperature suggests the existence of negative temperature co-efficient of resistance (NTCR) in the material. Studies of electric modulus show the presence of hopping conduction mechanism in the material with non-exponential-type of relaxation. The nature of variation of dc conductivity with temperature confirms the Arrhenius- and NTCR- types of behaviors of the material. The ac conductivity spectrum provides a typical-signature of an ionic conducting system, and is found to obey Jonscher′s universal power law.