Improved critical current densities in MgB2 tapes with ZrB2 doping

Abstract

Abstract:MgB 2 /Fe tapes with 2.5-15 at.% ZrBB 2 additions were prepared through the in situ powder-in-tube method. Compared to the pure tape, a significant improvement in the in-field critical current density Jc was observed, most notably for 10 at.% doping, while the critical temperature decreased slightly. At 4.2 K, the transport Jc for the 10 at.% doped sample increased by more than an order of magnitude than the undoped one in magnetic fields above 9 T. Nanoscale segregates or defects caused by the ZrB 2 additions which act as effective flux pinning centers are proposed to be the main reason for the improved Jc field performance. a) Author to whom correspondence should be addressed, E-mail: ywma@mail.iee.ac.cn 1 MgB 2 is considered as a possible substitute for Nb-Ti or high-T C oxide superconductors operated at around 20 K because of its high transition temperature (T C ) and weak-link free character. The low material costs, simple structure and small anisotropy are additional advantages of MgB 2 . Therefore, it is thought as the most promising candidate for engineering application, especially for magnetic resonance imaging (MRI) magnet which prefers to work at cryogen-free circumstances.However, critical current density (J C ) of MgB 2 decreases rapidly under magnetic fields compared to those for the Nb-based superconductors. MgB 2 is a two-gap structure material, and phonon scattering induced by the lattice distortions in this material is very pronounced. This suggests that the upper critical field (H C2 ) of MgB 2 can be enhanced by introducing electron-scattering defects. It has been demonstrated that C doped thin films have H C2 (0K) about 50 T [1].Various dopants [2-8] have been investigated, leading to a wide variation in the reported values of H irr and J C . In the case of ZrB 2 , we reported earlier that the improved J C value was observed in 5% ZrB 2 -doped MgB 2 tapes when sintered at 600°C [9]. Furthermore, an increase in HC2 from 20.5 T to 28.6 T and enhancement of H irr from 16 T to 24 T were obtained in the ZrB 2 doped bulk MgB 2 samples as compared to the binary sample at 4.2 K [10]. This means that ZrB 2 doping is a very promising method for MgB 2 tapes to get higher J C in high magnetic fields. Therefore, it is very necessary to carry out further investigation on the doping effect of this material due to the lack of systematic study. In this work, a series of ZrB 2 doped MgB 2 tapes were prepared using an in situ powder-in-tube (PIT) method. The highest J C values were achieved in samples with 10% ZrB 2 doping level, more than 11-fold improvement compared to the undoped tapes. The field dependence of J C decreased by the ZrB 2 doping, suggesting that pinning centers effective in a high-field region were possibly introduced.The detailed procedure for preparation of MgB 2 /Fe tapes has been reported elsewhere [11]. Mg (325 mesh, 99.8%), B (amorphous, 99.99%), and ZrB 2 (2-5 μm, 99%) powders were used as the starting materials. Mg, B powders were mixed with the nominal composition of 1:2, th...

Fabrication of the 19-filament Fe/Cu clad MgB2 wire via in situ powder-in-tube method

“…One can see that the onset T C and transition width (ΔT C ) for MgB 2 sample are 34.5 K and 4.8 K, respectively. Compared to our previous sample [16] using 99.99% purity B and 99.5% Mg as starting materials, a slight degradation of onset T C , about 1.8 K, was observed, which may be related to inferior MgB 2 crystallinity and worse grain connectivity caused by impurity from the 92% B powder. Accompanied by 5% excess Mg addition, the onset T C slightly degrades and the T C transition broadens as expected, reaching 34 K and 5.2 K, respectively.…”

“…As can be seen from Figure 2, there is a weak peak corresponding to Fe 2 B, suggesting that there was reaction between Fe layer and MgB 2 core at 700℃. Furthermore, the full width at half-maximum (FWHM) of peaks for both samples is slightly larger than that of the corresponding peaks for our pure sample using high purity B as starting materials [16] , the broadening of the FWHM indicates the poor MgB 2 crystallinity. The occurrence of Mg peak for Mg 1.05 B 2 sample ( Figure 2) suggests that 5% excess Mg in precursors is enough to compensate the Mg loss due to reaction with boric oxide and absorptive oxygen atoms.…”

Prospects for improving the intrinsic and extrinsic properties of magnesium diboride superconducting strands

“…Selected thin film data [3], [26,27], [34], [36] NbCu37+M ( Selected thin film data [3], [26,27], [34], [36] maleic anhyd. [41] SiC [42] ZrSi 2 [43] ZrB 2 [5,44] MgO [45] Mg 1.00 B 2 [38] Mg 1.15 B 2 [38] Selected thin film data [3], [26,27], [34] …”

Drawing induced texture and the evolution of superconductive properties with heat treatment time in powder-in-tubein situprocessed MgB2strands

“…These can be accomplished through: (i) site-substitution into the Mg sublattice by Zr [21,22], Na [23], or similar-sized cations [24][25][26][27], (ii) site-substitution into the B sublattice by C [28][29][30][31][32] (with regard to which we note that it has been difficult to distinguish t-he influence of substitution from effect of possible C-induced lattice strain [33][34]), and (iii) increasing the connectivity between MgB 2 grains (or grain clusters) to increase the efficiency of supercurrent flow [35][36][37][38].…”