Crossover from glassy to ferroelectric polarization behavior under a dc bias electric field in relaxor ferroelectrics

摘要

The remanent dielectric polarization P_r(T), as estimated from zero-field heated (ZFH) pyroelectric current between 10 and 295 K, was studied in the pyrochlore relaxor ferroelectric Cd_2Nb_2O_7 on approach' to the field-induced ferroelectric (FE) state both from an ergodic relaxor state (ERS) and a nonergodic glassy relaxor state (NERS). The measurements were done after field cooling (P_r~(FC)) and zero-field cooling (P_r~(ZFC)) a relaxor system to a given temperature far below the freezing temperature T_f, removing (applying) the bias, and subsequent ZFC (FC) to 10 K. P_r~(FC)(T) and P_r~(ZFC)(T) behave differently both in a weak and rather high dc bias electric field, which evidences the different character of the NERS developing in these regimes and the different predisposition of the NERS to a formation of the long-range FE ordering. The large splitting between P_r~(FC) and P_r~(ZFC) confirms the glassy nature of the NERS. For NERS-to-FE crossover, the critical field E_(cr)~(NERS) E_(cr)~(ERS), while at E_(cr)~(ERS) < E < E_(cr)~(NERS) the NERS first passes into an intermediate glass-and-FE state. The FE state field induced from ERS or NERS is inhomogeneous up to the higher bias fields, while the traces of the glassy state persist. It is found that a proper formation of the NERS and FE state in relaxors is prearranged during ZFC and FC through T_f.