Feng Jianqing

Influence of Cu Content in Precursor Powders on the Phase Evolution and Superconducting Properties of Bi-2212 Superconductors

Abstract Precursor powders of Bi 2.1 Sr 1.96 CaCu x O 8+δ (Bi-2212) high temperature superconductors with different nominal Cu ratios of x =2.0, 2.1, 2.2, 2.4 were fabricated by a modified co-precipitation process. The influences of Cu ratios on the phase evolution process during sintering were investigated. Bi-2212 thick films and single filament tapes were fabricated with dip-coating process and powder in tube process, respectively. Obvious influences of Cu ratios on the phase compositions, microstructures and superconducting properties were discussed. Results show that the initial Cu ratio can affect the thermodynamic properties of Bi-2212 phase, thus changing phase evolution process. With the increase of Cu ratio, the phase content of Bi-2201 decreases, while the content of AEC phase increases. The maximum critical current density is obtained in the x =2.2 film and tape simultaneously due to the proper phase composition and better texture structures.

Effect of Carbon and SiC Doping on Microstructures of MgB2 Bulks and Wires by a Two-Step Reaction Method

Abstract Carbon and SiC doped MgB 2 bulks and wires were fabricated by a two-step reaction method. The MgB 4 samples were sintered at 900 °C for 2 h in closed argon atmosphere, and then an appropriate amount of Mg powder was mixed with the ground MgB 4 powder to get MgB 2 green compacts, which were sintered at 750 °C for 2 h to get bulk samples or at 680 °C for 2 h to get wire samples in closed argon atmosphere. Carbon or SiC doped MgB 2 bulk samples were also prepared by conventional solid state sintering for comparison. The phase evolution and the microstructure of MgB 2 samples were characterized by means of X-ray diffraction (XRD) and scanning electron microscope (SEM). The SEM results indicate that the compactedness and the dopant distribution homogeneity of MgB 2 samples prepared by the two-step reaction method are improved obviously. The carbon doping can more effectively introduce the dopants into MgB 2 crystalline lattice and grain boundaries compared with SiC doping.