Synthesis and crystal chemistry of the new compounds GdBa4Cu3O8.5+delta and DyBa4Cu3O8.5+delta

Two new compounds, GdBa4Cu3O8.5+delta (Gd143), and DyBa4Cu3O8.5+delta (Dy14 3), were synthesized from precursors Gd2O3, DY2O3, BaO2, and CuO at 1000 de grees 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. Rietv eld refinement of x-ray powder diffraction data showed that Gd143 belongs t o the space group Pm3 while Dy143 belongs to the space group P23. The two s pace groups, Pm3 and P23, are very similar. Their main difference is that P 23 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 Gd1 43 and 8.10807 +/- 0.00010 Angstrom for Dy143. Superconducting quantum inte rference device (SQUID) measurement indicated that neither compound was sup erconductive down to 5 K.