Contrast anomaly of planar defects in synchrotron white-beam topography of Fe-doped KTa1−xNbxO3

The contrast anomaly of a set of planar defects in Fe-doped KTa1−xNbxO3 with a Curie point near room temperature has been studied by synchrotron white-beam X-ray topography. A striking wavelength-dependent characteristic of the defect contrast is shown by tuning the synchrotron radiation, and the contrast reversal of the planar defects is displayed in antiparallel reflections. The intense anomaly in contrast is interpreted in terms of anomalous dispersion associated with antiparallel domains.