Location of rare-earth atoms in isomorphous series of complex oxides by employment of difference Fourier syntheses based on X-ray powder profile analysis: La₃LnBaCu₅O_13+δ (Ln = Y, La, Nd or Gd) and LnBa₂Cu₃O_7±δ (Ln = Y, Nd, Pr, Gd or Dy)

Analysis of the X-ray powder diffraction profiles of an isomorphous series of inorganic solids has been carried out for two series of complex oxides: La₃LnBaCu₅O_{13 + δ} (Ln = Y, Nd or Gd) and LnBa₂Cu₃O_{7 + δ} (Ln = Y, Nd, Pr, Gd or Dy). In this method, profile and structure refinements of a reference compound are followed by a difference Fourier synthesis to locate the positional parameters of a substituent atom. A linear correlation exists between the Fourier peak height in the difference Fourier map and the atomic number of the substituent atom. By an analysis of relative peak height in the correlation plot, the extent of cation disorder, if any, can be determined.