Synthesis and crystal chemistry of the new compounds GdBa₄Cu₃O_8.5+δ and DyBa₄Cu₃O_8.5+δ

Two new compounds, GdBa4Cu3O8.5+delta (Gd143), and DyBa4Cu3O8.5+delta (Dy143), were synthesized from precursors Gd2O3, DY2O3, BaO2, and CuO at 1000 degrees C in an oxygen atmosphere. The oxygen stoichiometric value delta was found to be 0.68 for Gd143 and 0.6 for Dy143 by iodometric titration. Rietveld refinement of x-ray powder diffraction data showed that Gd143 belongs to the space group Pm3 while Dy143 belongs to the space group P23. The two space groups, Pm3 and P23, are very similar. Their main difference is that P23 does not have the inversion symmetry of Pm3. Both compounds have a cubic unit cell with a lattice parameter of 8.16528 +/- 0.00006 Angstrom for Gd143 and 8.10807 +/- 0.00010 Angstrom for Dy143. Superconducting quantum interference device (SQUID) measurement indicated that neither compound was superconductive down to 5 K.