X-Ray Dynamical Diffraction Contrast due to Inhomogeneous Impurity Distribution

A detailed investigation was made of the X-ray diffraction contrast arising at the boundary of two growth sectors of potassium dihydrogen phosphate (KDP) crystals with different impurity content when the boundary plane is perpendicular to the specimen surface. Topographs of reflected and transmitted beams have been taken in the symmetrical Lane case under conditions of both high and low absorption. In the high-absorption case, the contrast calculated on the basis of the Penning and Polder theory for a simplified model of lattice distortion is in good agreement with experimental observations. A simple rule is established for the determination of the sign of the lattice parameter difference from topographs taken with (hkl) and ((hkl) over bar) reflections.