Effect of electric field on dielectric response of PMN-PT thin films

Abstract

Electric field (ac and dc) induced complex dielectric properties of 0.7 Pb(Mg_1/3Nb_2/3)O₃-0.3 PbTiO₃ (PMN-PT) thin films were studied as a function of frequency at different temperatures. A non-linear behavior of dielectric susceptibility, with respect to the amplitude of the ac drive, was observed at lower temperatures. The magnitude of the dielectric constant measured at 1 kHz was increased from 2000 to 6000 with increasing ac signal amplitude from 0.5 to 10 kV/cm, while temperature of maximum dielectric constant (T_m) was observed to follow reverse trend at all frequencies. The relaxor nature of PMN-PT thin films was studied in terms of diffused phase transition along with frequency dispersion of temperature of dielectric maximum (T_m). Vogel-Fulcher relationship was used to analyze the frequency dependence of temperature of dielectric maximum (T_m). The dielectric constants (both real and imaginary) of PMN-PT thin films were observed to reduce with the application of external dc field. The external dc bias suppressed the frequency dispersion and increased the ferroelectric stability by increasing the transition temperature (T_m). The disappearance of relaxor nature in PMN-PT (70/30) films was attributed to manifestation of long-range order at higher bias voltage.