DIFFRACTION ANOMALOUS FINE-STRUCTURE ON FORBIDDEN AND SUPERLATTICE REFLECTIONS

The phenomenon of diffraction anomalous fine structure (DAFS) has been examined in relation to structural symmetry and is discussed for PbZr O3 in the space group Pbam. It is found that DAFS appears on the super lattice reflection, even if the intensity of the reflection is free fr om the anomalous dispersion of heavy atoms at the relevant absorption edges. For reflections that are forbidden by the glide symmetry, DAFS oscillation can be observed, unaffected by the influence of absorption and of X-ray absorption fine structure oscillation; the amplitude of DAFS oscillation depends on the polarization of incident X-rays. The r ole of DAFS signals in superstructure investigation is discussed with respect to highly absorbing crystals of finite size.