  Ferroelectric domain boundaries are quasi-two-dimensional functional
interfaces with high prospects for nanoelectronic applications. Despite their
reduced dimensionality, they can exhibit complex non-Ising polarization
configurations and unexpected physical properties. Here, the impact of the
three-dimensional (3D) curvature on the polarization profile of nominally
uncharged 180{\deg} domain walls in LiNbO3 is studied using second-harmonic
generation microscopy and 3D polarimetry analysis. Correlations between the
domain wall curvature and the variation of its internal polarization unfold in
the form of modulations of the N\'eel-like character, which we attribute to the
flexoelectric effect. While the N\'eel-like character originates mainly from
the tilting of the domain wall, the internal polarization adjusts its
orientation due to the synergetic upshot of dipolar and monopolar bound charges
and their variation with the 3D curvature. Our results show that curved
interfaces in solid crystals may offer a rich playground for tailoring
nanoscale polar states.
