Shear effects in lateral piezoresponse force microscopy at 180° ferroelectric domain walls

In studies using piezoresponse force microscopy, we observe a nonzero lateral piezoresponse at 180° domain walls in out-of-plane polarized, c-axis-oriented tetragonal ferroelectric Pb(Zr0.2Ti0.8)O3 epitaxial thin films. We attribute these observations to a shear strain effect linked to the sign change of the d33 piezoelectric coefficient through the domain wall, in agreement with theoretical predictions. We show that in monoclinically distorted tetragonal BiFeO3 films, this effect is superimposed on the lateral piezoresponse due to actual in-plane polarization and has to be taken into account in order to correctly interpret the ferroelectric domain configuration.