THE EFFECTS OF CS ADDITION AND DIFFERENT SINTERING CONDITIONS ON YSCO-123 SUPERCONDUCTORS MADE FROM PRECURSOR OR COMMERCIAL 123-POWDER

Bulk Y1Ba2Cu3O7-delta superconductors were prepared from initial mixtu res of a precursor and CsI or commercial 123 Hoechst powder and Csl wi th the nominal composition Y1Ba2Cu3CsxOy (X = 0, 0.05, 0.1, 0.2 and 0. 3). Different synthesis regimes were applied in order to determine the influence of normal or reduced oxygen pressure as well as vacuum when isothermal heating at 800 degrees C is performed during sintering. It was found that heating at 800 degrees C with reduced oxygen pressure favourably affects the J(c) and density of the samples in the case whe re 123 powder is used as the starting material. When the precursor is used the intensive dissociation of BaCO3 at low pressure leads to high er porosity and deterioration of the superconducting properties. Addin g Cs in small concentrations promotes higher J(c) and density of speci mens made from the precursor, but when commercial 123 powder is used, a negative effect is observed due to the chemical instability of the s uperconducting phase. Atomic absorption spectrometry reveals that the Cs disappears during sintering and, therefore, could be used in small concentrations as a fluxing additive without any risk of creating Cs-c ontaining impurity phases.