Quantitative investigation of domain structures by Berg-Barrett X-ray diffraction microscopy. II. Identification of domains

In Berg-Barrett micrographs of twinned crystals whose structure is slightly distorted from cubic, a characteristic pattern of white and dark bands appears due to small changes of orientation of the reflecting planes; the appearance of these bands depends on which lattice planes are used for reflection. The orientations of the crystallographic axes in the individual twin components can be determined from a knowledge of the relative magnitudes of the tilt angles in various twinned lattice planes, and from a study of the widths and contrast of bands in the images from different Bragg reflections from the same crystal face. This method has been developed for twins appearing in rhombohedral and tetragonal structures, and applied to antiferromagnetic NiO and ferroelectric BaTiO₃ crystals in order to identify microscopic domains.