Nonergodic Relaxor Research Articles

Nonlinear field dependence of the quasistatic and first harmonic dielectric response in relaxor materials

The quasistatic linear and nonlinear dielectric constants εs in lead magnesium niobate (PMN [111] and PMN [001]) crystals were investigated by means of the charge accumulation technique. The zero-field-cooled and field-cooled static susceptibilities show a crossover from a nonergodic relaxor to inhomogeneous ferroelectric behavior. At electric fields above the critical value contribution from the saturated spontaneous polarization was observed. The temperature dependence of the total third order nonlinear response was also determined along both axis.

Electric-field induced phase transitions in 9/65/35 PLZT ceramics

Transition lines between various phases in the electric-field temperature phase diagram of 9/65/35 PLZT ceramics were determined by measurements of the temperature and electric-field-dependent dielectric constant. Above the critical field Ec the dc bias electric field induces relaxor to the ferroelectric (FE) phase transition. Transition lines were found to depend on the direction of the approach — the temperature or dc bias field direction — to the FE phase. Also, a strong impact of the electric field on the stability of the FE phase with the increasing temperature was found. Below Ec the system exhibits a transition line between the ergodic and nonergodic relaxor state. The experimental results are compared with the results of a spherical random bond-random field model of relaxor ferroelectrics.

Electric-field–temperature phase diagram of the relaxor ferroelectric lanthanum-modified lead zirconate titanate

Transition lines between various phases in the electric-field--temperature phase diagram of 9/65/35 lanthanum-modified lead zirconate titanate ceramics were determined by measurements of the temperature and electric-field-dependent dielectric constant. Above a critical field ${(E}_{C})$ the dc bias electric field induces a transition from the relaxor (R) to the long-range ferroelectric (FE) phase. In the temperature direction of the approach to the FE phase the R-FE transition line was determined from the field-cooled--field-heated dielectric susceptibilities, while depolarization temperatures were obtained from the field-cooled--zero-field-heated dielectric susceptibilities. A considerably large shift was found for the above two R-FE transition lines demonstrating the strong impact of the electric field on the stability of the FE phase with increasing temperature. It was found that below ${E}_{C}$ ergodicity is broken due to the divergence of the longest relaxation time at the freezing temperature ${T}_{0}=259 \mathrm{K}.$ Hence the system exhibits a transition line between the ergodic (ER) and nonergodic (NR) relaxor state. In the dc bias field direction of the approach to the FE phase, the temperature dependence of ${E}_{C},$ i.e., the transition lines between ER or NR and FE phases were studied by measurements of the complex dielectric constant as a function of a dc bias field at several fixed temperatures. The experimental results are compared with the results of a spherical random bond-random field model of relaxor ferroelectrics.

Slow dynamics and ergodicity breaking in a lanthanum-modified lead zirconate titanate relaxor system

The freezing of the dynamic process in a 9/65/35 lanthanum lead zirconate-titanate (PLZT) ceramics has been investigated by measurements of the frequency-dependent complex dielectric constant and the quasistatic field-cooled (FC) and zero-field-cooled (ZFC) dielectric susceptibilities. It was found that the aging process is responsible for the difference in temperature variations of the FC static dielectric constant and the static dielectric constant determined in the dynamic ZFC experiment. Analysis of the complex dielectric susceptibility by a temperature-frequency plot has revealed that for an aged PLZT sample the ergodicity is broken due to the divergence of the longest relaxation time in the vicinity of 249 K, i.e., the temperature where the ferroelectric phase can also be induced by applying sufficiently high electric field. However, the bulk of the distribution of relaxation times was found to remain finite even below the freezing temperature. It is shown that the behavior of the relaxation spectrum and the splitting between the field-cooled and zero-field-cooled dielectric constants in PLZT relaxor is qualitatively similar to what was observed in the lead magnesium niobate (PMN) relaxor and is reminiscent of the nonergodic behavior reported in various spin glasses. Moreover, the temperature dependence of the third order nonlinear susceptibility indicates a glassy rather than ferroelectric multidomain nature of the nonergodic relaxor state in both PMN and PLZT systems.