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

Abstract Ti-sheathed monocore MgB 2 wires with improved magnetic critical current density ( J c ) 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 J c values at 5 K and fields of 2 T, 5 T, and 8 T are 4.1 × 10 5  A/cm 2 , 7.8 × 10 4  A/cm 2 , and 1.4 × 10 4  A/cm 2 , respectively. At 20 K and fields of 0.5 T and 3 T, the J c values are about 3.6 × 10 5  A/cm 2 and 3.1 × 10 4  A/cm 2 , respectively, which are much higher than those of the Fe-sheathed mono-core MgB 2 wires fabricated with the same in situ PIT process and under the same fabricating conditions. It appears that the overall J c 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 J c in the Ti-sheathed MgB 2 wires can be strongly suppressed by MgO impurities and micro-cracks.