Polarization analysis to separate the resonance contribution to the allowed X-ray reflections

It has been shown that channels of resonant X-ray scattering with a change in polarization can be present in allowed Bragg reflections. The measurement of the energy and azimuthal dependences of Bragg reflections with a change in polarization makes it possible to study resonant diffraction in crystals of symmorphic groups, which are often used to describe the symmetry of functional materials. This can be effectively used to study structural changes in phase transitions or external impacts, as well as to separate contributions to resonant scattering from crystallographically nonequivalent positions of atoms. A sharp increase in the intensity of the scattering of $\pi$-polarized radiation into $s$-polarized radiation has been demonstrated by the simple example of lowering the symmetry of the SrTiO$_3$ crystal as a result of the transition from the cubic phase to the tetragonal one. It has also been shown that the study of the circular X-ray dichroism of Bragg reflections can be used instead of the polarization analysis of scattered radiation.