Effects of Silver Addition on Critical Current Densities and Mechanical Properties in Bulk MgB₂

Abstract

The present study focuses on the effects of Ag addition on the critical current density (J c ) and the mechanical performance of disk-shaped MgB 2 bulk superconductors. MgB 2 samples with varying Ag contents of 0, 2, 4, 6, 8, and 10 wt% were sintered at 775°C for 3 h in Ar atmosphere. The J c values were improved with Ag addition, in that the sample with 4 wt% Ag showed the highest J c value of 295 kA cm À2 at 20 K and self-field. The respective J c values of the same sample were 430, 360, and 238 kA cm À2 in self-field, 0.5 T, and 1 T at 7 K. These values are the highest so far reported in bulk MgB 2 materials. Scanning electron microscopy showed that silver and silver oxide particles are embedded in the voids. As a result, the mechanical performance at room temperature was improved with Ag addition. We also confirmed the presence of nanometer-sized AgMg 3 particles, which may be responsible for high flux pinning and improved mechanical performances.

Flux Pinning and Superconducting Properties of Bulk MgB2 with MgB4 Addition

“…This is because the control of MgB 4 in situ formation is difficult and once formed, MgB 4 disturbs stoichiometry of MgB 2 matrix. A similar scenario was observed when we tried to create Ag–Mg pinning centers in situ . We had to optimize the excess Mg required for maximum performance.…”

Modelling of Critical Current Density of Sintered Ag Added Bulk MgB2

“…Similarly, improvements had reported that Ag doping significantly enhances MgB 2 formation rate in MgB 2 wires with enhanced properties [22]. On the other hand, these results indicate that Ag addition to MgB 2 can be one of the ways to improve not only mechanical properties [17,[21][22][23][24] but also flux pinning; the critical temperature remains almost unchanged. It is also positive that Ag does not react with MgB 2 and can help to reduce cracks density like in cuprates [25].…”

“…More recently, EDX analysis by TEM had lucidly confirmed that Ag enriched phase distributed in MgB 2 matrix obtains a composition in close to AgMg 3 [21] and its size and dispersion in MgB 2 matrix is somewhat dependent on initially added silver content. Further, it was also confirmed by AFM observations that nanometer sized AgMg 3 particles were dispersed in MgB 2 matrix [17]. Therefore, it is essential to estimate the flux pinning behavior of bulk MgB 2 material with Ag addition and more details are presented below.…”

“…• C/h, the more details for the processing of these materials are reported elsewhere [17]. The microstructure of these samples was studied with a scanning electron microscope (SEM) and chemical compositions were analyzed by energy dispersive X-ray spectroscopy (EDX).…”

Production and Characterization of Bulk MgB2Material made by the Combination of Crystalline and Carbon Coated Amorphous Boron Powders

“…To improve the critical current density of the MgB2 material, a variety of processing techniques have been developed and studied in terms of commercially usefulness [9,10]. On the other hand, to improve the critical current density of these materials a variety of dopants [11][12][13][14] were adopted and very successful results were observed, especially using carbon-based dopants, e.g., carbon, boron carbide, carbon nanotubes, carbohydrates or hydrocarbons, graphene oxide, carbon-coated boron powders, etc. [15][16][17][18][19].…”