X-ray topographic study of antiphase domain boundaries in ferroelectric ferroelastic GdDy(MoO4)3 crystals. II. Evaluation of the additional translation vector

Antiphase domain boundaries (APB’s) can be considered as planar defects introducing a phase shift between the structure factors of both domains. Two different geometries of APB’s are considered here, corresponding respectively to Laue–Bragg and Laue–Laue cases for x-ray propagation. Comparison between experimental and computer simulated x-ray topographic sections in both cases leads to an evaluation of the additional translation vector Δf at the APB of the order of a/30 resulting from a local expansion of the lattice. A simple interpretation for this result is given.