Dielectric response of the relaxor ferroelectric Pb(Mg1/3Nb2/3)O3 in the nonergodic state after a DC electric field is turned off

Abstract

The Pb(Mg1/3Nb2/3)O3 (PMN) relaxor system is used as an example to analyze the temperature dependences of the low-frequency dielectric permitivity (ɛ′(T)) measured during zero-field heating (ZFH) from T = 10 K to T = 300 K after using different field cooling (FC) conditions. No changes in the temperature dependences of the permittivity have been detected during the transition from a nonergodic relaxor state (NERS) into an ergodic relaxor state (ERS) (at T f ≈ 216 K). However, the difference Δɛ′(T) between the curves corresponding to different field cooling conditions in the same electric field has different shapes and different values below and above T → (T f + 9 K)− (for E dc = 1.52 kV/cm). The reduced permittivities ɛ′r(T, f) recorded under different cooling conditions are shown to change their behavior when passing through T = T f + 9 K. In NERS, these curves diverge: the stronger the field (0 ≤ E dc ≤ 3 kV/cm), the larger the divergence. In ERS, however, the ɛ′r(T, f) curves coincide under different cooling conditions irrespective of the field. The character of the changes in Δɛ′(T) and ɛ′r (T, f) during the NERS-ERS transition is frequency-independent. The difference in the behavior of the dielectric response during ZFH after cooling in different (ZFC, FC) modes (even in a weak field), for both transition through T f and cooling down to T = 10 K, indicates different NERSs forming under these conditions. The contribution to ɛ′(T) from slowly relaxing regions (ω ∼ 0.1 mHz), whose polarization is reoriented after the field is turned off, is responsible for the fact that, during the NERS-ERS transition, the ɛ′r(T, f) curves coincide at a temperature that is higher than T = T f.