Effects of BaO_2 addition on the properties of melt-processed YBa_2Cu_3O_(7-delta)

摘要

Samples of YBa_2Cu_3O_(7-delta) having about 30 percent YBa_2Cu_3O_(7-delta) , were prepared with a melt-process method by adding B_2O_3 up to 0.5 wt percent to the oxides. The structural and superconducting properties of the samples were studied by x-ray diffraction, x-ray fluorescence, scanning electron microscope, magnetization and magneto-optic techniques. B_2O_3 additions during the melt-processing enlarge intergrain regions that weaken the conduction links between the grains. Tc drops by 1.0-6.0 K, and at 50 K Jc decreases from about 1.6 x 104 to 1.8 x 103 A cm~(-2) with B_2O_3 additions up to 0.5 wt percent. A secondary peak was observed in the Jc versus field plot of the boron-free sample that decreases with boron additions. At 50 K the intragrain Jc values of the boron-free sample were about 12 percent higher than the intergrain Jc value, and such differences increase with B_2O_3 additions. These observations, together with the enlargements of the intergrain regions with B_2O_3 additions, suggest that most of the boron atoms take part and reside at grain boundaries.