High Critical Current Density of a MgB 2 Bulk Superconductor High-pressure Synthesized Directly from the Elements
- PDF / 329,705 Bytes
- 3 Pages / 612 x 792 pts (letter) Page_size
- 26 Downloads / 189 Views
We report the property studies of a MgB2 superconductor with high critical current density. The MgB2 superconductor was readily fabricated through a direct high-pressure synthesis of the respective elements. The obtained high-density MgB2 undergoes a sharp superconducting transition at 39 K. The bulk critical current density (Jc) of the sample was calculated on the basis of Bean’s critical state model, and rather high critical current densities over a wide temperature range were obtained in comparison with the ambient prepared samples. The results highlight that high-pressure sintering would be a promising way to produce and search for this kind of intermetallic boride and the related superconductors.
The discovery of 39 K superconductivity in a MgB2 intermetallic compound1 opens a new way to search for new superconductors with higher Tc. The MgB2 compound ranks as having the record high Tc reached in intermetallic superconducting compounds, just below the high-Tc cuprates2,3 and the C60 system.4 The rather higher Tc of the MgB2 superconductor raises a challenge for mechanism studies and brings new hopes to both the applications of superconducting compounds and the search for new superconducting materials particularly in the boride system. Although the MgB2 superconductor is readily obtained as a chemical reagent, it is usually in powder form, which makes it difficult for physical property measurements and general usages. During the past decades, high-pressure synthesis has proven to be a very effective method to fabricate new solid phases5 that are either unavailable or hard to approach at ambient conditions. In particular, high-pressure synthesis plays a very important role in building up the novel high-Tc superconductors.6,7 Recently Takano et al. reported the highpressure sintering of commercial MgB2 powder, which significantly improved the superconducting properties of the materials.8 Li et al. succeeded in the direct synthesis of the MgB2 superconductor from Mg and B powders, yielding a 39 K MgB2 superconductor.9 Here we present the results of the critical current density measurements of the MgB2 bulk superconductor, which has been obtained through the further improved direct-element synthesis under high pressure. The optimized synthesis leads to a high-quality reproducible bulk MgB2 superconductor with sharp superconducting transition and high critical current density comparable to those of high-pressure sintered commercial MgB2.8 J. Mater. Res., Vol. 17, No. 3, Mar 2002
In the experiments the powders of magnesium (80 mesh, 98.5% above purity) and boron (360 mesh above, 5N purity) were used as starting materials. The stoichiometric Mg and B powders in molar ratio 1:2 were carefully mixed in the protection of N2 atmosphere. The mixture being installed into the Pt cell to avoid contamination was put into a BN tube and then inserted into a graphite sleeve, which serves the electric heater in the following high-pressure synthesis. A 1000ton cubic anvil type high-pressure equipment was utilized to conduct the h
Data Loading...
