  The anomalously large dielectric aging in ferroelectric partially deuterated
potassium dihydrogen phosphate (DKDP) is found to have multiple distinct
mechanisms. Two components cause decreases in dielectric response over a
limited range of fields around the aging field. A large fraction of this aging
occurs on time scales of ~1000s after a field change, as expected for a
hydrogen/deuterium diffusion mechanism. A slower component can give almost
complete loss of domain-wall dielectric response at the aging field after weeks
of aging. There is also a particularly unusual aging in which the dielectric
response increases with time after rapid cooling.
