X-ray diffuse scattering in SrTiO₃ and model of atomic displacements

The scattering intensity of synchrotron radiation in a compact three-dimensional volume of the reciprocal space (sinθ_max/λ = 0.6283 Å⁻¹) of an SrTiO₃ single crystal has been measured at temperatures of 115, 130 and 293 K. The curvilinear features of the diffuse pattern were modelled according to the displacements of both cations correlated along the axis [001]_cub (where the subscript cub denotes the cubic structure). The results show that Sr²⁺ is displaced from the ideal positions along the crystallographic axis [001]_cub, forming a short chain composed of about three Sr²⁺ ions along [001]_cub, while the Ti⁴⁺ ions are moved in the directions [111]_cub, or alternatively [101]_cub or [011]_cub. The Ti⁴⁺ displacements are also correlated along [001]_cub, forming a similarly short chain.