Rietveld refinement of crystal chemistry of RBa4Cu3O8.5+δ (R=rare earth) Original Research Article

Rietveld refinements of X-ray powder diffraction data were performed on RBa4Cu3O8.5+δ (R143) compounds, where R=Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb, to determine their oxygen content and distribution, lattice parameter, and space group. The total oxygen content was found to oscillate with the atomic number of the rare earth elements. The compounds with R having even atomic numbers have higher total oxygen content than those with R having odd atomic numbers. With increasing atomic number of the rare earth element, the oxygen distribution on the O3 and O4 sites changes from uniform (e.g. Sm143) to primarily on the O3 sites. The lattice parameter decreases smoothly with increasing atomic number, which is caused by the monotonic decease in the ionic radii of the rare earth elements. However, the ionic radius does not have significant influence of the total oxygen contents. The refinement also revealed that the correct space group of Sm143 and Eu143 and and , respectively.