Mechanical Softness of Ferroelectric 180° Domain Walls

This effect is observed in different ferroelectric materials (${\mathrm{LiNbO}}_3$, ${\mathrm{BaTiO}}_3$, and ${\mathrm{PbTiO}}_3$) and with different morphologies (from single crystals to thin films), suggesting that the effect is universal. We propose a theoretical framework that explains the domain wall softening and justifies that the effect should be common to all ferroelectrics. The lesson is, therefore, that domain walls are not only functionally different from the domains they separate, but also mechanically distinct.