[en] In recent years, there has been increasing interest in dielectric and electrostrictive behaviour of relaxor ferroelectrics, which can be distinguished from normal ferroelectrics by diffuse phase transition and strong frequency dependence of the dielectric properties. The ferro-paraelectric phase transition (T_m) and all the related properties in these systems are characterized not by abrupt changes, but rather by gradual diffuse changes, which occur over a wide temperature range. Among the various electrostrictive materials, Pb(Mg_1/3Nb_2/3)O₃ (PMN)-based materials have carried special attention because of their better dielectric and electrostrictive properties. These materials have some features analogous to magnetic spin glasses and the Vogel-Fulcher relation are often used for describing the observed temperature dependence of cluster dynamics. Because of this properties, some of modified PMN ceramics are considered to be promising for fabrication of multiplayer capacitors (MLCs), electrostrictive transducer etc. The admittance spectroscopy using the variation of real part of admittance (Y) versus imaginary part of Y at room temperature shows glassy nature of the compounds. The frequency variation of impedance at different temperatures, show the bulk conductivity of the material increasing with a rise in temperature