Effects of MgO impurities and micro-cracks on the critical current density of Ti-sheathed MgB2 wires

Department of Mechanical Engineering, University of Houston, Houston, Texas, United States
Physica C Superconductivity (Impact Factor: 1.11). 06/2007; 457(1-2):47-54. DOI: 10.1016/j.physc.2007.02.013

ABSTRACT Ti-sheathed monocore MgB2 wires with improved magnetic critical current density (Jc) have been fabricated by in situ powder-in-tube (PIT) method and characterized by magnetization, X-ray diffraction, scanning electron microscopy and electrical resistivity measurements. For the best wire, the magnetic Jc values at 5 K and fields of 2 T, 5 T, and 8 T are 4.1 × 105 A/cm2, 7.8 × 104 A/cm2, and 1.4 × 104 A/cm2, respectively. At 20 K and fields of 0.5 T and 3 T, the Jc values are about 3.6 × 105 A/cm2 and 3.1 × 104 A/cm2, respectively, which are much higher than those of the Fe-sheathed mono-core MgB2 wires fabricated with the same in situ PIT process and under the same fabricating conditions. It appears that the overall Jc for the average Ti-sheathed wires is comparable to that of the Fe-sheathed wires. Our X-ray diffraction and scanning electron microscopy analysis indicates that Jc in the Ti-sheathed MgB2 wires can be strongly suppressed by MgO impurities and micro-cracks.

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    ABSTRACT: The effects of sintering temperature on the superconducting properties of Ti-sheathed MgB2 wires have been studied. The wires were fabricated by in situ powder-in-tube (PIT) method and characterized by x-ray diffraction, magnetization, scanning electron microscopy and transport measurements. Samples were sintered for 30 minutes at the following temperatures: 650° C, 700° C, 750° C, 800° C, and 850° C. It is found that the cores of these wires are almost in pure MgB2 superconducting phase, indicating that the Ti-sheath does not react with Mg or B. The superconducting transition temperature Tc decreases from 36 K to 34.2 K with the decrease of the sintering temperature from 850° C to 650° C. At 5 K and 20 K, critical current density Jc peaks up for samples sintered at 800° C, which is in sharp contrast with previously reported result that for Fe-sheathed MgB2 wires, Jc peaks up at sintering temperature of 650° C.
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