Effect of BaFe12O19 nanoparticles doped on the properties of single domain GdBa2Cu3O7-δ high-temperature superconductors

The flux pinning performance of the superconductor is important for the applications of the GdBa2Cu3O7-δ superconductor bulk. To introduce the suitable secondary phase into the GdBa2Cu3O7-δ matrix is an important way to enhance the performance of flux pinning. By using top-seeded melt texture growth process, single domain GdBa2Cu3O7-δ superconductor bulks (20 mm in diameter) doping with different quantities of BaFe12O19 nano-particles (12O19(x=0, 0.2 mol%, 0.4 mol%, 0.8 mol%)+ 10 wt% Ag2O+ 0.5 wt% Pt. The effects of different quantities of BaFe12O19 nano-particles on superconducting properties and microstructure are also investigated. The result shows that the critical current density, JC, with 0.2 mol% BaFe12O19 additions reaches a maximum value in the zero field, which is about 5.5 × 104 A/cm2. And the critical current density JC, almost increases in the whole field compared with those of the undoped bulks. The microstructure and chemical composition of GdBa2Cu3O7-δ bulk with BaFe12O19 nano-particles are implemented by the SEM-EDS technique. It is found that BaFe12O19 nano-particles keeps a similar form to that of the precursor in the final superconductor bulk. The average size of Gd2BaCuO5 particles is reduced from 1.4 μm in the undoped bulk to 0.79 μm in the bulk with 0.2 mol% BaFe12O19 nano-particles. We suggest that BaFe12O19 nano-particles may form effective magnetic flux centers in the bulks, which affects the homogeneous distribution and refinement of Gd2BaCuO5 particles. Therefore, the improvements in the critical current density and the trapped field are observed in the GdBa2Cu3O7-δ bulk with low-level doped content. The superconducting transition temperature TC, can be maintained at around 92.5 K. However, with the addition of 0.4 mol% BaFe12O19 nano-particles, the critical current density and superconducting transition temperature decrease obviously. It indicates that the excessive addition of BaFe12O19 nano-particles may affect the superconductivity properties to reduce the critical current density, JC. The result indicates that the low-level content BaFe12O19 nano-particles can be an effective second phase for the improvement of the GdBa2Cu3O7-δ superconductor bulks, which is very important for the further enhancing the superconducting properties of GdBa2Cu3O7-δ bulks by introducing the flux pinning of nano-particles.