Polycrystalline bulks of Bi 2 Sr 2 Ca 1−x K x Cu 2.0 O 8+δ (Bi-2212) with x = 0, 0.05, 0.10 and 0.15 were fabricated by the spark plasma sintering technique. The influences of K doping on the microstructures, electronic structures, as well as the related superconducting properties, were systematically investigated. The XRD analyses confirmed that K + ions have successfully substituted into the matrix of Bi-2212, and lead to a systematical change of lattice parameters. Due to the change of thermodynamic properties, bulks with higher density, larger grain size and better texture structures were obtained after doping. Therefore, ac susceptibility measurement revealed the optimization of intergrain connections, which lead to the optimization of both selfand in-field critical current density, J c of this system. The optimization of microstructures also caused the enhancement of surface pinning. Based on the enhancements of both intergrain connections and flux pinning properties, an obvious improvement of critical current density was obtained with the optimal doping content of K = 0.05. Meanwhile, Bi-2212 single filament tapes with K doping content of 0 and 0.05 were also fabricated by the powder-in-tube process. The XRD patterns also proved the successful doping of K ions in the Bi-2212 matrix. The critical current density J c , measured by the transport method under the magnetic field from 0 to 20 T at 4.2 K, proved the effectiveness of K doping on the enhancement of flux pinning properties of Bi-2212.
A hybrid protocol including particle-in-cell (PIC) ions and Boltzmann electron distribution is developed to simulate plasma immersion ion implantation (PIII) into an S-shaped bar inside a grounded cylindrical cage consisting of a mesh. A multiple-grid system with three cell confinements is adopted to achieve sufficient accuracy and acceptable computational time. The simulation results reveal that the implantation fluence distribution along the major curvature is more uniform than that obtained by conventional PIII.
The phase evolution of Bi-2223 precursor powder prepared by spray pyrolysis method is studied with different heat treatment parameters. The results show that the reaction temperature and phase composition of precursor powder depend on heat treatment atmosphere. Phase assemblage of (Bi,Pb)-2212, AEC, CuO, and small Bi-2201 can be obtained by heat-treated in N 2 -0.1%O 2 atmosphere. For precursor powder, there is sufficient reaction process at 770 • C, and the dimension of Bi-2212 phase increases rapidly with the increase of heat treatment temperature and time. The dimension of AEC phase also increases by extending heat treatment time. As a balance among phase assemblage, dimension of particle and adequate reaction, a reasonable precursor powder can be obtained by heat-treated at 770 • C for 12 h-16 h in N 2 -0.1%O 2 atmosphere. Critical current of 37-filament Bi-2223 tape is about 120 A, which confirms that these heat treatment parameters are reasonable.
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