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High permittivity dielectrics ceramics are often used for commercial multilayer ceramic capacitors, actuators applications, and is highly promising materials for dynamic random access memory (DRAM) and microelectromechanical systems (MEMS) applications due to its very stable, high insulating characteristic against voltage. Many studies have been conducted to enhance the above mentioned properties and most of the improvements have been achieved by doping with a small quantity of additives with some ferroelectric perovskite lead and lead free compounds. Especially, Na 0.5 Bi 0.5 TiO 3 (NBT) is one of the promising materials for environmental friendly application in compare to lead based composition. Extensive studies have been made on NBT based relaxor ferroelectric ceramic with a simultaneous substitution of Ba 2+ and Zr 4+ at Asite and B-site having led to the establishment and acceptance of the "space charge" model on the basis of explaining their structure and dielectric properties. A Polycrystalline 0.92(Bi 0.5 Na 0.5 )Ba 0.08 Z 0.04 T 0.96 O 3 (0.08BNBZT) material has been prepared by conventional solid state reaction method. X-ray diffraction pattern reveals a tetragonal structure having lattice parameters. The diffuseness parameter =1.59 has been established the relaxor nature. The dielectric relaxation obeyed the Vogel-Fulcher relation. Impedance spectroscopy is a convenient tool to evaluate the contribution of electrical components such as grain (g) (bulk), grain-boundary (g b ) or polarization phenomena, which influences the device properties of a material. Conductivity studies in the materials obey the Jonscher's power Law in frequency (45Hz -5MHz), temperature (35 0 C-600 0 C) range.

In this manuscript, the structural and dielectric properties of Gadolinium (Gd3+) substituted at Bi-site of SrBi2-xGdxNb2O9 (x= 0.0, 0.4, 0.6 and 0.8) prepared by using solid state reaction are studied. XRD analysis revealed the formation of single phase with orthorhombic structure in SBN and Gadolinium modified SBN. It is found that cell parameters and volume were decreased with increase of Gd3+ ion concentration in SBN. SEM analysis revealed that the samples possess well defined needle shaped grains. The grain size of SBN was hindered by the presence of Gd3+ ion at Bi-site. The growth of single phase layered perovskite structure was confirmed from FTIR and Raman spectroscopy. The dielectric properties of Gd3+ ion doped SBN ceramics are studied as a function of frequency (50Hz-1MHz) from room temperature to 500ºC. It is observed that phase transition temperature (Tc) decreased from 430ºC to 330ºC with increase of frequency due to incorporation of Gd3+ ion in SBN. The broadness of peaks and decrease in Tc indicate the transition from a normal ferroelectric to ferroelectric-relaxor type. The study on variation of tanδ with temperature at different frequencies indicates that tanδ has larger values at higher temperatures. Further, the diffuseness parameter (γ) has been computed for all the compositions.

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