High temperature memory in (Pb/La)(Zr/Ti)O_3 as intrinsic of the relaxor state rather than due to defect relaxation

TL;DR

This study demonstrates that high-temperature memory in relaxor ferroelectric PLZT is intrinsic to the relaxor state itself, rather than caused by defect migration, challenging previous assumptions about the origin of such memory effects.

Contribution

It provides evidence that high-temperature memory in PLZT relaxors is intrinsic and not due to mobile defects, unlike in non-relaxor compositions where defect migration causes memory.

Findings

Memory is reduced by mobile defects like vacancies and charges.

Memory persists above the susceptibility maximum in La-rich relaxors.

Defect migration causes memory in non-relaxors, but relaxors have intrinsic memory.

Abstract

It has been recently shown that the memory of multiple aging stages, a phenomenon considered possible only below the glass transition of some glassy systems, appears also above that temperature range in the relaxor ferroelectric (Pb/La)(Zr/Ti)O_3 (PLZT). Doubts exist whether memory at such high temperature is intrinsic of the glassy relaxor state or is rather due to migration of mobile defects. It is shown that the memory in the electric susceptibility and elastic compliance of PLZT 9/65/35 is not enhanced but depressed by mobile defects like O vacancies, H defects and mobile charges resulting from their ionization. In addition, memory is drastically reduced at La contents slightly below the relaxor region of the phase diagram, unless aging is protracted for long times (months at room temperature). This is considered as evidence that in the non relaxor case memory is indeed due to slow migration of defects, while in the La rich case it is intrinsic of the relaxor state, even above the temperature of the susceptibility maximum.