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

Four new RBa4Cu3O8.5+δ (R143) compounds, where R=Ho, Er, Tm, and Yb, were synthesized from precursors Ho2O3, Er2O3, Tm2O3, Yb2O3, BaO2, and CuO at 1000 C in an oxygen atmosphere. The oxygen stoichiometric value δ 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 diffraction data showed that all the compounds belong to the space group Pm anti 3. The compounds have a cubic unit cell with lattice parameters of 8.09485±0.00007 A for Ho143, 8.08236±0.00005 A for Er143, 8.07670±0.00008 A for Tm143, and 8.06198±0.00005 A for Yb143. SQUID measurements indicated that none of the compounds was superconducting above 5 K. (orig.)