Direct x-ray synchrotron imaging of strains at 180° domain walls in congruent LiNbO₃ and LiTaO₃ crystals

We present direct evidence for wide regions of strain on length scales of many micrometers associated with 180° domain walls in congruent LiNbO₃ and LiTaO₃ crystals. Strain contrast in symmetric high-resolution diffraction images of these crystals in Bragg geometry arises in part from curvature in the basal planes (0001) across a domain wall as well as from lateral variation in the lattice spacing of the basal planes extending over many micrometers in going across a wall.