Switching behaviour of modulated ferroelectrics I: kinetics of the field-induced lock-in transition of Rb2ZnCl4

Abstract

The structural changes of ferroelectric Rb₂ZnCl₄ have been studied in real time under the influence of pulsed electric fields by high-resolution γ-ray diffraction close to the lock-in transition at 198.3 K. A well-defined field-induced switching between the incommensurate and the commensurate phase is observed only in virgin crystals on a time-scale of milliseconds. Crystals aged under high electric fields, however, exhibit an intermediate diffuse phase that is attributed to pinning effects of discommensurations, i.e. the walls of nano-domains in the incommensurate phase. Surprisingly, the incommensurate phase itself is stabilized and the transition into the ferroelectric phase is shifted to lower temperatures as soon as the frequency of the cycled electric field is increased. This unusual finding is discussed in terms of stress fields associated with the motion of discommensurations.