In Situ 3D Observation of the Domain Wall Dynamics in a Triglycine Sulfate Single Crystal upon Ferroelectric Phase Transition

We present the first in situ 3D observation of domain wall dynamics close to a ferroelectric–paraelectric phase transition, which we obtain via second‐harmonic generation microscopy (SHGM). Showing a pure second‐order phase transition at its Curie temperature of 49 °C, triglycine sulfate (TGS) is a model ferroelectric material to study such phase transitions. After annealing, in TGS various qualitatively different domain patterns, e.g., stripes or small lenticular domains, have been reported so far. By applying SHGM, we can show that these findings do not necessarily contradict each other. In fact, qualitatively different domain patterns may coexist in the same TGS sample at the same time.