In situ imaging of domain walls in ferroelectric single crystals by instant polarized light microscopy

Ferroelectric domain walls separate regions of uniform polarization in ferroelectric materials, and their controlled manipulation, such as through electric poling, is essential for enhancing the electromechanical performance of advanced ferroelectric devices. While most existing imaging techniques only examine static domain structures at the pre- or post-poling state, real-time, in situ, and non-destructive visualization of internal domain wall dynamics during electric poling using a simple implementation remains a significant challenge. In this work, we present a simple and accessible optical technique, instant polarized light microscopy (IPOLπ), for through-volume, single-shot, and in situ observation of domain wall evolution during electric poling. Demonstrated on [110]-oriented Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals, IPOLπ enables direct observation of polarization dynamics during alternating current poling and electrical depoling. The method reveals the formation of layered domain structures initiating at sample edges and progressing inward, as well as the correlation between optical birefringence changes and electrical current response. This low-cost, robust technique provides a powerful tool for studying real-time domain wall behavior, offering new insights into structure-property relationships in functional ferroelectric crystals.