Aging Dynamics in Ferroelectric Deuterated Potassium Dihydrogen Phosphate

Anomalously large dielectric aging is found in the high-susceptibility plateau ferroelectric regime of ~95% deuterated potassium dihydrogen phosphate (DKDP). Much less aging is found in non-deuterated KDP. Optical images of the DKDP domain structure show no dramatic change during aging. Small changes in electric field restore the pre-aged susceptibility, but the previous aging almost recovers after returning to the aging field. Susceptibility vs. field can show memory of at least two prior aging fields. Rectifying non-linear susceptibility develops for fields slightly above or below a prior aging field. Aging effects are not fully erased even by brief heating above the Curie point, indicating a role for diffusion of hydrogen to the domain walls, leaving changes in disorder that can survive temporary absence of domain walls. Abrupt random-sign steps in polarization on cooling are accompanied by increases in susceptibility, indicating competition between large-scale domain-wall interaction effects and effects of local interactions with disorder.