White-beam synchrotron-radiation and conventional X-ray topography of GdCa4O(BO3)3:Y

The defect structure of gadolinium–calcium oxoborate single crystals highly doped with 22% Y, Gd0.78Y0.22Ca4O(BO3)3, is studied using X-ray transmission topography both with the conventional source and synchrotron radiation. Straight dislocation diffraction contrasts, white or black, depending on absorption and on its changing while the diffraction vector is reversed, are observed. A model of formation of dislocation contrast is proposed in the case of intermediate absorption.