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Tham khảo tài liệu 'the discovery of type ii superconductors part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 216 Superconductor Ed a d 7 Ed s d 1 0.8 0.6 0.4 0.2 0 1 0.8 0.6 0.4 0.2 70 K s 73 K 75 K A 77 K 78 K o 80 K ffl 82 K 1 84 K X 86 K 88 K 90 K 0.8 0.6 0.4 0.2 a 65 K 68 K a 70 K a 73 K B 75 K A 77 K 80 K 82 K 84 K 86 K 88 K J 90 K 0.4 1 1 0f I I I I I I I I I I I I I I Illi TiO B 65 K 68 K Bl 70 K B 73 K B 75 K A 77 K 80 K 82 K 84 K 86 K 88 K A 90 K 0.8 0.6 0.2 0 0.3 mol TiO. q 2 I B 65 K 68 K B 70 K B 73 K B 75 K A 77 K 80 K 82 K 84 K 86 K 88 K Â 90 K 0 . 0.2 0.4 0.6 0.8 1 ho h Fig. 10. Normalized pinning force density f Fp Fpmax as a function of reduced field h B Birr of NEG-123 samples with the same 35 mol content of Gd-211 70 nm but various contents of TiO2 for temperatures from 65 to 90 K. 7. Flux pinning in NEG-123 with MoO3 nanoparticles The size reduction of non-superconducting pinning centers significantly below 100 nanometer range proved that mesoscopic precipitates size of a few tens of nanometers were able to exceptionally enhance flux pinning up to very high temperatures. Although levitation experiments at 90.2 K have already been realized with NEG-123 superconductors doped by Zr-based or TiO2 based nanoparticles the safety margins needed for practical applications require a further improvement in flux pinning in these materials. Recent experiments clarified that this task could be realized with MoO3 nanoparticles. Figure 11 shows the temperature dependence of the dc magnetic susceptibility in the ZFC and FC modes in magnetic field of 1 mT for NEG-123 35 mol Gd-211 1 mol CeO2 and 0.5 mol Pt samples with varying contents of MoO3. All the samples exhibited a sharp superconducting transition around 1 K wide with a high onset Tc. The onset Tc systematically decreased from 93.2 to 92 K with increasing MoO3 content. The critical current density at 77 K of the MoO3 added NEG-123 composites with 35 mol Gd-211 secondary phase is presented in Fig. 12 left . The remnant critical current density dramatically increased for 0.1 mol MoOs but decreased thereafter. The