Nuclear and magnetic diffuse scattering of neutrons from β-ferrous oxalate dihydrate

Neutron diffraction experiments were carried out at 300 K and 4.2 K on polycrystalline samples of the αand β forms of FeC₂O₄.2D₂O. Diffuse scattering has been observed from faulted structure of the β form. The intensity formula given by Takaki & Sakurai [Acta Cryst. (1976), A32, 657–663] for X-ray diffraction from a one-dimensionally disordered crystal has been adapted to studies of diffuse nuclear and magnetic scattering of neutrons. The structure of β-FeC₂O₄.2D₂O has been interpreted in terms of the stacking faults of four kinds of layers. Essentially the same behaviour for the magnetic susceptibility and intensity of magnetic peaks versus temperature was found for both forms.