Ferroelectric phase transitions in epitaxial antiferroelectric PbZrO3 thin films

The archetypical antiferroelectric, PbZrO3, remains poorly investigated in its thin film form. While most of the studies on PbZrO₃ thin films focused on films thicker than 100 nm, only a few have been dedicated to epitaxial thin films with lower thicknesses. Here, the signature of an antiferroelectric state of 45-nm-thick epitaxial thin films of PbZrO₃ is established by observing the characteristic structural periodicity of antiparallel dipoles at the atomic scale, combined with clear double hysteresis of the polarization-electric field response related to antiferroelectric–to–ferroelectric phase transitions. Furthermore, on-field piezoresponse force microscopy imaging allows to visualize the induced ferroelectric domains. Surprisingly, while the antiferroelectric state is identified as the ground state, temperature-dependent measurements show that a transition to a ferroelectric-like state appears in a large temperature window (100 K). Atomistic simulations further confirm the existence, and provides the origin, of such ferroelectric state in the films. Electric-field-induced ferroelectric transitions are also detected by the divergence of the piezoresponse force microscopy response, which is less sensitive to leakage than standard capacitive readout for thinner films. Using this technique, we further reveal the signature of a ferroelectric ground state for 4-nm-thick PbZrO₃ films. Compared to bulk crystals, these results suggest a more complex competition between ferroelectric and antiferroelectric phases in epitaxial thin films of PbZrO₃. Finally, I will show how using an appropriate buffer oxide layer as an artificial single crystal substrate with large unit-cell parameters can be used to stabilize fully-strained high-quality epitaxial PbZrO₃ thin films.