Pattern analysis and interpretation of scattering from short-range order stacking in the layered composite crystal 2H-Na_xCoO₂·yD₂O (x ≃ 0.35, y ≃ 1.3)

Information about the features of Bragg reflections and/or diffuse streaks was obtained through simulation of a neutron powder diffraction pattern based on the model used in a successful analysis of the superconductor 2H-Na_xCoO₂·yD₂O (x ≃ 0.35, y ≃ 1.3). Intensity distributions were calculated based on a superstructure expression of a commensurate composite crystal model, where the structures of the CoO₂ part (a₁ = b₁ = 2.82 Å) and the guest (a₂ = b₂ = 3.26 Å) with short-range order stacking are described on a cell of A = B = 2a₁ = 3^1/2a₂ = 5.64 Å, and with alternate stacking based on c = 4.9 Å. It is shown that the most conspicuous diffuse reflection band corresponds to the main reflection scattering of the guest sheet, with local maxima at half-integer positions of ζ′ based on the stacking distance 2c, and that the Bragg diffraction components of the host and guest are coherent in terms of the peak height at integer ζ′′ based on 4c.