Metastable states and defect density waves in modulated ferroelectrics

ABSTRACT

The influence of defects on the phase behaviour of Rb-doped K₂ZnCl₄-single crystals is studied using high-resolution gamma-ray diffractions in combination with in situ dielectric impedance spectroscopy. It is shown that the interaction between strain fields near discommensurations within the incommensurate phase and impurity ions lead to the formation of defect density waves. On rapid cooling, these are unable to relax and persist within the commensurate phase thus acting as an intrinsic memory. Hence, a metastable re-entrant incommensurate phase is observed on heating at temperatures well below the normal lock-in temperature that is found in equilibrium studies.

KEYWORDS:

• Modulated phase
• lock-in transition
• defects
• polar nanodomains
• ferroelectrics
• defect density wave