Upper critical field, irreversibility field, and critical current density of powder-in-tube-processed MgB₂/Fe tapes

Abstract

We fabricated pure and SiC-added MgB2/Fe composite tapes using a MgH2 starting powder and applying heat treatments at 600–900 °C and systematically investigated their superconducting properties. For both the pure and SiC-added tapes, the critical temperature (Tc) increased with increasing heat-treatment temperature due to the improved crystallinity of MgB2.The SiC addition decreased the Tc but increased the slope of the Bc2–T and Birr–T curves, d Bc2/d T and d Birr/d T, for all heat-treatment temperatures. The d Bc2/d T and d Birr/d T of the pure tape decreased with increasing heat-treatment temperature from 600 to 700 °C because of the longer coherence length associated with the improved crystallinity. However, the SiC addition significantly decreased the heat-treatment temperature dependences of d Bc2/d T and d Birr/d T. At a temperature of ∼20 K, which is easily obtained using a cryocooler, the Birr is governed by both the Tc and d Birr/d T. The Birr of a pure tape at 20 K decreased with increasing heat-treatment temperature from 600 to 700 °C, but the Birr of the 10 mol% SiC-added tape increased with the temperature. These behaviours can be explained by the heat-treatment temperature dependence of the Tc and d Birr/d T. At 20 K the highest Birr of 10 T was obtained under the conditions of a 10 mol% SiC addition and heat-treatment temperature of 900 °C. This Birr at 20 K is comparable to that of commercial Nb–Ti at 4.2 K. The 10 mol% SiC-added tape heat treated at 900 °C and the 5 at.% SiC-added tape heat treated at 800 °C showed Jc (MgB2 core) values higher than 104 A cm−2 at 20 K in 5 T.

Effect of aromatic hydrocarbon addition onin situpowder-in-tube processed MgB2tapes

“…It was reported that, for the SiC-added tape, the a-axis length shrank, while the c-axis did not change due to the substitution of the carbon from SiC powder for boron. 9 Similar changes of the a-and c-axis lengths were also observed for C 6 H 6 -, C 10 H 8 -, and C 4 H 4 S-added tapes, although the decrease of the a-axis length is almost independent of the amount of C 6 H 6 . This result indicates that the substitution of carbon for boron also occurs in the aromatic hydrocarbon-added tapes.…”

The doping effect of multiwall carbon nanotube on MgB2∕Fe superconductor wire

“…This result can be explained by the improved crystallinity of the MgB 2 core, indicating that the grain size increases with sintering temperature. 21 The FWHM behavior of long CNT doped wire as a function of sintering temperature was similar to that of pure wire. However, FWHMs of short CNT doped wire increased with annealing temperature.…”

Strongly enhanced current-carrying performance in MgB2 tape conductors by C60 doping

“…The resistance measurements were carried out on Physical Properties Measurement System (PPMS) up to 9 T using small pieces of MgB 2 core after peeling off the Fe sheath or on a 20 T magnet using Fe sheathed MgB 2 tapes. [22] The transport I c at 4. is an indication of the carbon substitution for boron, [18] which is further proved by the depression of the critical transition temperature (T c ) of the C 60 doped samples. The C substitution to B site has a great impact on the carrier density and impurity scattering.…”

“…[20] Figure 2 [22] For instance, at 20 K, H irr was nearly 10 T for C 60 doped MgB 2 tapes sintered at 800 °C. This is in accordance with XRD analysis that C has been substituted into MgB 2 lattice.…”