Modelling of cation displacements in SrTiO₃ by means of multi-energy anomalous X-ray diffuse scattering

X-ray diffuse scattering of SrTiO₃ has been measured at two photon energies, the first just below the absorption edge and the second far from the K absorption edge of strontium, in order to vary the atomic scattering factor of the strontium cations. It is shown that two different models of cation displacement comply with the single-energy diffuse scattering patterns, because single-energy diffuse scattering provides only ambiguous information on the directions of displacement of the Sr²⁺ and Ti⁴⁺ cations. However, the application of multi-energy anomalous diffuse scattering determines unambiguously that the Sr²⁺ cations are moved from their ideal positions in the [100] direction and the Ti⁴⁺ cations are shifted in {111} directions.