Dielectric characteristics of perovskite-structured high-temperature relaxor ferroelectrics: The BiScO₃-Pb(Mg_1/3Nb _2/3)O₃-PbTiO₃ ternary system

A new compositional family of relaxor ferroelectrics was investigated based on the high-temperature Bi(Me)O₃-PbTiO₃ ferroelectric perovskite family. Compositions were fabricated near an estimated morphotropic phase boundary (MPB) of the xBiScO₃-yPb(Mg_1/3Nb _2/3)O₃-zPbTiO₃ (xBS-yPMN-zPT) ternary system exhibiting high-temperature relaxor properties of T_max ∼250°-350°C and ε_max ∼10 000-24 000 at 1 kHz. Analysis of the low-field a.c. permittivity by a Vogel-Fulcher type dependence enabled key parameters of activation energy, E_A, and freezing temperature, T_f, to be determined. The remanent polarization was studied over a broad temperature range and was observed to show classical ferroelectric square loop hysteresis behavior at temperatures T<T_f while slim loop hysteresis behavior was observed at temperatures T _f<T<T_max. Pyroelectric current measurements were made and integrated to determine macroscopic polarization-temperature dependence, and were in excellent agreement with the hysteresis data. The macroscopic polarization was found to drop off rapidly near the freezing temperature, T_f. At temperatures T>T_max, the deviation temperature, T_D, was obtained from Curie-Weiss analysis and found to be ∼600°C. A comparison of characteristic electrical properties was made between the high-temperature perovskite relaxors and the classical complex lead relaxor compound, Pb(Mg_1/3Nb_2/3)O₃ (PMN).