Effect of ZrO2 doping on structure and superconducting properties of sintered DyBaCuO ceramics

The effect of ZrO2 addition (1 wt% and 5 wt%) on the superconducting properties of sintered DyBa2Cu3Oy ceramics was studied. The doping was found to assist the formation of secondary phase inclusions such as Dy2BaCuO5 (211), BaZrO3 and CuO. No traces of Zr in the 123 grains (matrix) were revealed. Doping by ZrO2 favoured the formation of a fine-grain microstructure, the amount of clean boundaries strongly increasing compared with the undoped composition. Doping by 1 wt% ZrO2 resulted in a substantial increase in the critical current density Jc. The samples with the addition of 5 wt% ZrO2 showed the best flux pinning in a magnetic field. Such behaviour seems to be associated with a substantial increase in proportion of clean boundaries and the presence of fine facets and regularly distributed dislocations in these boundaries in the doped samples. The measured dependence of the critical current Ic on temperature close to Tc indicated that weak links at grain boundaries behave as a network of superconductor-insulator-superconductor (SIS) junctions in all compositions, except for the composition with 1 wt% ZrO2 which showed superconductor-normal metal-superconductor (SNS) behaviour.