Zhang Xianping

Simple One-Step Synthesis and Superconducting Properties of SmFeAsO1–xFx

The recent discovery of superconductivity in REFeAsO (RE, rare-earth metal) has generated enormous interest because these materials are the first non-copper oxide superconductors with critical temperatures Tc exceeding 50 K as well as upper critical fields well above 100 T. However, for these new superconductors, very complicated synthesis routes, such as the complex two-step synthesis or high-pressure sintering, are required. Furthermore, there is the toxicity and volatility of arsenic to consider, sometimes a sealed quartz tube of arsenic exploded during annealing. We present a new method for producing high-temperature SmFeAsO1–xFx superconductors by using a one-step sintering process. Superconducting transition with the onset temperature of 54.6 K and high critical fields Hc2(0) ≥ 200 T were confirmed in SmFeAsO0.7F0.3. At 5 K and at self field, critical current densities Jc estimated from the magnetization hysteresis using the whole sample size and the average particle size have reached 8.5 × 103 and 1.2 × 106 A/cm2, respectively. Moreover, Jc exhibited a very weak dependence on magnetic field. This simple and safe one-step synthesis technique should be effective in other rare earth derivatives of iron-based superconductors.

Development of iron-based superconducting materials for applications

The discovery of superconductivity in iron pnictides has generated a great deal of research interest, not only in basic physics, but also in the field of applied superconductivity. It has been confirmed that the pnictides have peculiar physical properties including an unconventional pairing mechanism. This brings an opportunity to discover new kind of superconductor with high transition temperature. On the other hand, compare to the cuprate, the iron-based superconductors have a rather high upper critical field ( H c2) and low anisotropy. These properties are very attractive for practical application. An overview of the development of iron-based superconductors is presented in this article. The crystal structure of various iron-based superconductors is presented. At the same time, the fabrication techniques of iron-based tapes and films for “1111”, “122”, “11” type of pnictide are reviewed. Some promising features such as a high critical current density in tapes and thin films under high magnetic fields have been clarified. Finally, we summarize and compare the features and properties of the pnictide materials with other classical cuprate and MgB2 superconductors.

Fabrication and Properties of Aligned Sr(0.6)K(0.4)Fe(2)As(2) Superconductors by High Magnetic Field Processing

We fabricated a c—axis aligned Sr0.6K0.4Fe2As2 superconductor using a two-step magnetic field procedure. The effect of the magnetic fields on the structure and superconducting properties of Sr0.6K0.4Fe2As2 is investigated using x-ray diffraction and magnetic measurements. The degree of orientation of the samples is about 0.39 for the c axis and 0.51 for ab-plane orientation, as evaluated from the Lotgering factor of x-ray diffraction. This technology may be useful in a variety of potential applications, including preparing iron-based superconducting bulks and wires with high critical currents.

Enhancement of Critical Current Density and Flux Pinning in Acetone and La2O3 Codoped MgB2 Tapes

MgB2 tape samples with simultaneous additions of acetone and La2O3 were prepared by an in-situ processed powder-in-tube method. Compared to the pure and single doped tapes, both transport Jc and fluxing pinning are greatly improved by acetone and La2O3 codoping. Acetone supplies carbon into the MgB2 crystal lattice and increases the upper critical field, while the La2O3 reacts with B to form LaB6 nanoparticles as effective flux pining centers. The improvement of the superconducting properties in codoped tapes can be attributed to the combined effects of improvement in Hc2 and flux pinning.