Observation of strong virtual scattering under three-beam (220, 371) X-ray diffraction in TeO2 single crystal

A strong effect of virtual scattering has been experimentally observed when studying the nearly coplanar three-beam (220, 371) X-ray diffraction in a paratellurite single crystal under high-resolution double-crystal X-ray diffraction using MoKα1 radiation. One characteristic feature of this effect is that the angular dependence of the first (strong) reflection intensity and its shape barely change in the three-beam range of parameters, whereas very strong changes are observed for the second (weak) reflection not only in the three-beam range but also far beyond it, which is related to the variation in the two-beam diffraction parameter due to virtual scattering. The changes observed are asymmetric and make it possible to determine the triplet combination of structure-factor phases.