Aging effect in paraelectric state of ferroelectrics: Implication for a microscopic explanation of ferroelectric deaging

Most ferroelectric materials exhibit aging effect (a time-dependent change in physical properties) in their ferroelectric state; however, aging is not reported to exist in the paraelectric state. In this letter we report the existence of a "paraelectric aging effect" in Mn-doped (Ba _0.80 Sr_0.20) TiO₃ ceramics. We found that when the paraelectric state is formed from an aged ferroelectric state through a reverse ferroelectric transition, the paraelectric state shows a gradual increase in the dielectric permittivity and decrease in dielectric loss with time. Such paraelectric aging effect exists only in acceptor-doped samples, not in undoped samples. The kinetics of the paraelectric aging follows a simple relaxation function with activation energy of 0.43 eV. Our results suggest that the paraelectric aging stems from the migration of oxygen vacancies, being the same as the case of ferroelectric aging. We show that such a migration is driven by a symmetry-conforming short-range ordering tendency of point defects. Such a microscopic mechanism also provides a microscopic explanation for the well-observed "ferroelectric deaging effect."