Effect of deoxygenation on the weak link behavior of YBCO superconductors

A systematic study of the weak- link behavior for YBa2Cu3O7-d polycrystalline samples has been done using the electrical resistivity and AC susceptibility techniques.The experiments were performed with two samples of similar grain, a sample of well-coupled grains, and a deoxygenated sample in such a way that the oxygen mostly come from the intergrain region. Analysis of the temperature dependence of the AC susceptibility near the transition temperature (Tc) has been done employing Bean critical state model. The observed variation of intergranular critical current densities(Jc)with temperature indicates that the weak links are changed from superconductor- normal metal-superconductor(SNS) for well-coupled sample to superconductor-insulator- normal metal-superconductor(SINS) type of junctions for the deoxygenated sample.These results are interpreted in terms of oxygen depletion from grain boundaries, which in turn decreases the intergranular Josephson coupling energy with a consequent decrease ofpinning of the intergranular vortices.