Non-Ising domain walls in c-phase ferroelectric lead titanate thin films

Ferroelectrics are technologically important, with wide application in micromechanical systems, nonlinear optics, and information storage. Recent discoveries of exotic polarization textures in these materials, which can strongly influence their properties, have brought to the forefront questions about the nature of their domain walls: long believed to be primarily Ising, with locally null polarization. Here, combining three complementary techniques - second-harmonic generation microscopy, piezoresponse force microscopy, and transmission electron microscopy - to cover all the relevant length scales, we reveal the Néel character (non-Ising polarization oriented perpendicular to the wall) of 180° domain walls in c-phase tetragonal ferroelectric lead titanate epitaxial thin films, for both artificial and intrinsic domains at room temperature. Furthermore, we show that variations in the domain density - detected both optically and via local piezoresponse and then quantified by radial autocorrelation analysis - can give us insight into the underlying defect potential present in these materials.