Rietveld refinement of crystal chemistry of RBa4Cu3O8.5+delta (R = rare earth)

Rietveld refinements of X-ray powder diffraction data were performed on RBa 4Cu3O8.5+delta (R143) compounds, where R = Sm, Eu, Gd, Th, Dy, Ho, Er, Tm, and Yb, to determine their oxygen content and distribution, lattice paramet er, and space group. The total oxygen content was found to oscillate with t he atomic number of the rare earth elements. The compounds with R having ev en atomic numbers have higher total oxygen content than those with R having odd atomic numbers. With increasing atomic number of the rare earth elemen t, 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 smoo thly with increasing atomic number, which is caused by the monotonic deceas e in the ionic radii of the rare earth elements. However, the ionic radius does not have significant influence of the total oxygen contents, The refin ement also revealed that the correct space group of Sm143 and Eu143 and P2 (3) over bar and Pm (3) over bar, respectively. (C) 2001 Elsevier Science L td. All rights reserved.