The contribution of the "extrinsic" polarizations to the dielectric tunability of Pb (Mg _1/3 Nb _2/3) _1-x Ti _x O ₃ relaxor ferroelectrics

Pure perovskite Pb(Mg _1/3Nb _2/3) _1-xTi _xO ₃ (x = 0, 0.01, 0.03, 0.05, 0.07, 0.09) ceramics were prepared using a two-stage solid state reaction process. With the increase of Ti content, the dielectric tunability and dielectric loss at x = 0.09, 25 kV/cm and 300 K reached a maximum 91% and 0.09, respectively. High dielectric tunability 82% with low dielectric loss 0.007 was obtained at x = 0.05, indicating that it is a promising tunable material. The Lorentz fit of the temperature dependence of the dielectric permittivity and the measurement of the temperature dependence of the depolarization current density showed that polar nanoregions are related to the dielectric tunability properties of these relaxor ferroelectric ceramics _. The Landau-Ginsberg-Devonshire and multipolarization-mechanism model fitted results of the electric field dependence of the dielectric permittivity showed that the contribution of the "extrinsic" polarizations including "reorientation of nanopolar clusters" and the "motion of the cluster interphase boundaries or domain-wall motions" to the dielectric tunability properties increased with the increase of Ti content. These results provide a clear understanding to the complicated dielectric response in a family of high-tunability ceramics and a key to the high tunability of ferroelectrics with low loss under dc electric field.