Voltage-driven ferroelectric domain dynamics in (K,Na)NbO3 investigated by in situ transmission electron microscopy

Abstract

Ferroelectric domain dynamics is at the heart of any ferroelectric-based application. In situ transmission electron microscopy (TEM) offers an exciting opportunity to directly image ferroelectric switching and domain dynamics, revealing phenomena that might be concealed in macroscopic measurements. Here, we investigate the voltage-driven response of the mobile, needlelike domains and domain walls (DWs) of a (K,Na)NbO3 single crystal (KNNsc) using in situ TEM in a miniaturized capacitor. Our experimental results reveal that the immobile DWs can act as random bound pinning centers, pinning an area of up to 0.35 μm2. The edge of the sample can promote the nucleation of new domains. Domain growth and coalescence are not always continuous but can be interrupted at a certain voltage in favor of fine domain splitting and the formation of nanoscale domains. Other discontinuities are generated in the functional response when two orthogonal, needlelike domains meet and soft-pinning events occur. These findings shed light on the kinetics of ferroelectric domains and are probably not limited to KNNsc, being applicable to other perovskite-based ferroelectric materials where a needlelike domain morphology is present or where mobile and immobile DWs coexist.