Use of the Rietveld technique for estimating cation distributions

The use of the Rietveld full-profile refinement technique to estimate cation distributions is exemplified by a neutron powder diffraction study of the farringtonite-type solid solution γ-(Zn_0.70Fe_0.30)₃(PO₄)₂, with five- and six-coordinated cation sites. A review of similar studies (neutron or Guinier–Hägg X-ray data) of phases with the farringtonite, sarcopside, Ni₂P₄O₁₂ or olivine structure is given. The accuracy is discussed in terms of K_D distribution coefficients and metal–oxygen distances. Some investigations of olivines based on X-ray single-crystal data are reviewed for comparison.