Tracing the depolarization field-induced backswitching and domain shape transformation in lithium niobate at the nanoscale

Controlling the domain structure in ferroelectric crystals offers a powerful means of tailoring their functional properties, such as conductance, piezoresponse, and non-linear optical behavior. In particular, maintaining the stability of artificially written domain patterns is crucial for the performance of ferroelectric devices in memristor applications. Spontaneous polarization reversal, or backswitching, remains one of the most elusive challenges, as it reshapes domains and alters current pathways along domain walls. Here, we directly track in situ the nanoscale evolution of the morphology of a single in-plane domain on the non-polar surface of a lithium niobate single crystal during polarization backswitching, using non-contact Kelvin probe force microscopy. Combined with finite element simulations, our results show that the field distribution at the domain base and apex governs the onset of backswitching, leading to complex and asymmetric shape transformations. The interplay between depolarization and screening electric fields is shown to influence ferroelectric domain stability, providing a strategy for controlling the performance of devices based on domain-wall conduction.