Crystal structure and chemistry of four new RBa4Cu3O8.5+delta (R = Ho, Er,Tm and Yb) compounds

Four new RBa4Cu3O8.5+delta (R143) compounds, where R=Ho, Er, Tm, and Yb, we re synthesized from precursors Ho2O3, Er2O3 Tm2O3,Yb2O3, BaO2, and CuO at 1 000 degrees C in an oxygen atmosphere. The oxygen stoichiometric value delt a was found to be 0.50 for Ho143, 0.53 for Er143, 0.79 for Tm 143 and 1.01 for Yb143 by iodometric titration. Rietveld refinement of X-ray powder diff raction data showed that all the compounds belong to the space group Pm (3) over bar. The compounds have a cubic unit cell with lattice parameters of 8.09485+/-0.00007 Angstrom for Ho143, 8.08236+/-0.00005 Angstrom for Er143, 8.07670+/-0.00008 Angstrom for Tm143, and 8.06198+/-0.00005 Angstrom for Y b143. SQUID measurements indicated that none of the compounds was supercond ucting above 5 K. (C) 1998 Elsevier Science S.A. All rights reserved.