Analyzing structure factor phases in pure and doped single crystals by synchrotron X-ray Renninger scanning

X-ray multiple diffraction has been applied to study the substitutional incorporation of Mg²⁺ ions into NSH crystals (nickel sulfate hexahydrate, NiSO₄·6H₂O). Intensity profiles provide information on invariant phases, while angular positions of the multiple diffractions allow accurate determination of lattice parameters. By increasing the atomic disordering only of O^2- sites in model structures of doped NSH, the sense and magnitude of induced phase shifts match those necessary to justify the observed changes in the intensity profiles. Causes of disordering and lattice parameter variation are discussed. Although the amount of extra oxygen disordering is relatively large with respect to the small difference in the ionic radii of the metallic ions, this disordering is beyond the resolution power achievable by analyzing diffracted intensities of isolated reflections, such as in standard crystallographic techniques.