Temperature-Selective Relaxation Spectra for Aging, Memory, and Rejuvenation in Relaxor Ferroelectrics

Abstract

After an isothermal hold, a relaxor ferroelectric may look nearly unaged when it is cooled further, yet recover the earlier aging signal on reheating. Several holds can leave several such signals. This behavior follows from a simple model in which the measured polarization is coupled to a positive distribution of slow structural modes. The free energy is bounded, and the auxiliary dynamics obeys fluctuation–dissipation relations at fixed temperature. Eliminating the slow coordinates gives a causal and passive memory kernel with nonnegative dielectric loss. For a changing temperature, the kernel depends on two times and on the whole thermal path; the internal coordinates keep their states as the sample is cooled and reheated. Within this setting, cumulative aging occurs when the active spectra at different temperatures overlap strongly. Weak overlap lets the response rejuvenate at low temperature, while modes frozen after a stop recover their visibility on reheating and produce a memory notch. Well-separated spectral windows give approximately additive multiple-stop memories. A single scalar Debye mode cannot store several independently recoverable stops with one fixed set of parameters. Synthetic temperature cycles examine waiting time, probe frequency, ramp rate, spectral width, and Arrhenius or Vogel–Fulcher kinetics. Digitized PLZT and PMN–PT curves provide limited checks of notch shape and location. The construction gives a common dynamical description of aging, rejuvenation, and memory, while leaving the microscopic identity of the slow modes open. **Keywords** Relaxor ferroelectrics; dielectric aging; temperature-selective memory; rejuvenation; multiple-stop memory; relaxation spectra; two-time memory kernels; dielectric response; fluctuation–dissipation theorem; passivity.