Effects of the choice of different ionization level for scattering curves and correction for small preferred orientation in Rietveld refinement: the MgAl₂O₄ test case

The effects of the choice of oxygen scattering curves with different ionization levels and of the number of spherical harmonics terms used to correct for preferred orientation are discussed in the case of the Rietveld refinement of MgAl₂O₄ spinel. Results indicate that Rietveld refinements, and not only single-crystal analyses, are influenced by the choice of the scattering curves, at least in the case of very simple ionic structures. Improvements are observed both in agreement indices and in displacement parameter modelling by the use of an almost fully ionized model. On the contrary, the choice of the order of spherical harmonics prevalently affects the fractional u coordinate.