Effects of B₂O₃ addition on the properties of melt-processed YBa₂Cu₃O_7−δ

Abstract

Samples of YBa2Cu3O7−δ, having about 30% Y2BaCuO5, were prepared with a melt-process method by adding B2O3 up to 0.5 wt% 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. B2O3 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 × 104 to 1.8 × 103 A cm−2 with B2O3 additions up to 0.5 wt%. 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% higher than the intergrain Jc value, and such differences increase with B2O3 additions. These observations, together with the enlargements of the intergrain regions with B2O3 additions, suggest that most of the boron atoms take part and reside at grain boundaries.

Effect of boron doping in the microwave surface resistance of neutron irradiated melt-textured Y1.6Ba2.3Cu3.3O7−x samples

“…4; Rn is the normal-state value of the surface resistance obtained from Eq. This finding is ascribable to an increase of the effective penetration depth, which in granular samples is ruled by the intergrain field penetration depth, and is consistent with the observation that part of B atoms resides at the grain boundaries reducing the intergrain Josephson current [21].…”

“…This finding has been ascribed to a reduction of the charge carries due to an increase of the defect density. On the other hand, several authors [14,21,22,23] have suggested that dopants as Li and B can substitute Cu atoms in the Cu-O chains, breaking their continuity and, consequently, reducing their ability to transfer holes to the superconducting CuO 2 planes. So, the ρ increase associated to the H c2 decrease, we obtained in Y-12, may be due to the defect-induced reduction of carrier density.…”

“…Topal et al [16,17,21] have investigated the effects of thermal-neutron irradiation and B doping in a series of melt-textured YBCO samples containing pre-irradiation defects due to inclusion in the YBCO-123 phase of a certain amount of non-superconducting YBCO-211 phase, present as particles of micrometric dimensions uniformly distributed over the sample. In order to introduce B atoms, they added B 2 O 3 powder after calcinating the 211 and 123 phases.…”

“…In order to introduce B atoms, they added B 2 O 3 powder after calcinating the 211 and 123 phases. Investigating the unirradiated samples, it has been shown that the only addition of B 2 O 3 enlarges the intergrain regions, weakening conduction links between grains and lowering both T c and the critical current density, J c [21]. However, in the same paper, it has been highlighted a reduction of lattice parameters by 0.1-0.2% with B 2 O 3 addition up to 0.2-0.5 wt%, suggesting that some B atoms substitute copper atoms, probably in the Cu-O chains.…”

Effect of boron substitution on the crystallographic structure and superconducting properties in Y1‐xBxBa2Cu3Oy system

“…Recently, B 2 O 3 addition during Bi Pb 2 Sr 2 Ca 2 Cu 3 O 10 (Bi-2223) synthesis was shown to promote the growth of the high-phase by inducing more partially melted liquid phase of the Bi-based superconductors. These additions up to 0.01 wt % are reported to increase the critical current density c of Bi-2223 ceramics and silver-sheathed tapes [5]. Studies of boron effects on the YBaCuO system are very limited.…”