纳米微粒BaFe12O19掺杂对单畴超导块材GdBa2Cu3O7-δ性能的影响

Effect of BaFe_(12)O_(19) nanoparticles doped on the properties of single domain GdBa_2Cu_3O_(7-δ) high-temperature superconductors

磁通钉扎性能对GdBa_2Cu_3O_(7-δ)超导块材的实际应用具有重要的影响,而引入合适的第二相粒子可以改善GdBa_2Cu_3O_(7-δ)超导块材的磁通钉扎性能.本文采用顶部籽晶熔融织构法成功地制备出纳米微粒BaFe_(12)O_(19)(<100 nm)掺杂的超导块材,样品的最终组分为Gd123+0.4 Gd211+x BaFe_(12)O_(19)(x=0,0.2 mol%,0.4 mol%,0.8 mol%)+10 wt%Ag_2O+0.5 wt%Pt.通过研究不同掺杂量的BaFe_(12)O_(19)微粒对GdBa_2Cu_3O_(7-δ)超导块材微观结构和超导性能的影响,结果表明当掺杂量为0.2 mol%时,样品的临界电流密度几乎在整个外加磁场下都有明显的提高.在零场下,临界电流密度达到5.5×104A/cm2.纳米微粒BaFe_(12)O_(19)不仅可以保持掺杂前的化学组成,作为有效的钉扎中心存在于超导块材中,并且能够改善Gd_2BaCuO_5粒子的分布和细化Gd_2BaCuO_5粒子,使Gd_2BaCuO_5粒子的平均粒径由未掺杂时的1.4μm减小到掺杂后的0.79μm,进而提高了超导块材的临界电流密度和俘获磁场,明显提高了GdBa_2Cu_3O_(7-δ)超导块材的超导性能.临界温度TC也有所提升,并能够维持在92.5 K左右.该结果为进一步研究纳米磁通钉扎中心的引入并改善GdBa_2Cu_3O_(7-δ)超导块材的性能有着重要的意义.

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 （〈100 nm） are successfully fabricated. The final compositions of the bulk are Gd123 ＋ 0.4 Gd211 ＋ xBaFe12O19（x= 0, 0.2 mol%, 0.4 mol%, 0.8 mol%） ＋ 10 wt% Ag2O ＋ 0.5 wt% Pt. The effects of different quantities of BaFel2O19 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 × 10^4 A/cm^2. 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 1.4μm in the undoped bulk to 0.79 μm in the bulk with 0.2 tool% 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.