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-t itanate (PLZT) ceramics has been investigated by measurements of the freque ncy-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 var iations of the FC static dielectric constant and the static dielectric cons tant determined in the dynamic ZFC experiment. Analysis of the complex diel ectric 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 whe re the ferroelectric phase can also be induced by applying sufficiently hig h electric field. However, the bulk of the distribution of relaxation times was found to remain finite even below the freezing temperature. It is show n that the behavior of the relaxation spectrum and the splitting between th e field-cooled and zero-field-cooled dielectric constants in PLZT relaxer i s qualitatively similar to what was observed in the lead magnesium niobate (PMN) relaxer and is reminiscent of the nonergodic behavior reported in var ious spin glasses. Moreover, the temperature dependence of the third order nonlinear susceptibility indicates a glassy rather than ferroelectric multi domain nature of the nonergodic relaxer state in both PMN and PLZT systems. [S0163-1829(99)01101-7].