Oxygen plasma effects on zero resistance behavior of Yb,Er-doped YBCO (123) based superconductors

Rare-earth doped YBa₂Cu₃O_7-δ samples were synthesized starting from the corresponding oxides Y₂O₃, Yb₂O₃, Er₂O₃, CuO as well as Ba(OH)₂ by heating to 950 C under air. The doping concentrations were adjusted to 15 % Yb, 7 % Er and 20 % Yb, 15 % Er, respectively, with respect to the yttrium content. The orthogonal phased (123) YBCO ceramics were exposed to an oxygen plasma for 140 and 380 min. Zero resistance temperature (T_c,0) was determined by measuring the resistivity-temperature dependence using a classical four point measurement approach. Under optimal conditions with respect to the material composition and the oxygen treatment an unusual high zero resistance temperature of 97.5 K (T_c,onset ∼ 101 K) was achieved. This represents an increase of T_c,0 by 7.5 K. The oxygen treatment could not be monitored by IR spectroscopy, X-ray fluorescence spectroscopy, and X-ray powder diffraction. The results showed good reproducibility. (Copyright copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)