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Enhanced critical current density in MgB 2 prepared by reaction of MgB 4 and Mg

2013; Wiley; Volume: 210; Issue: 3 Linguagem: Inglês

10.1002/pssa.201228752

1862-6319

K. L. Tan, Kean Pah Lim, akbar halim, Soo Kien Chen,

Iron-based superconductors research

Abstract Instead of reacting B and Mg powders, MgB 4 was used as precursor to react with Mg to obtain the polycrystalline samples of nominal composition Mg x B 2 ( x = 1.2, 1.5, and 1.7). Upon increasing the sintering temperature to 750 °C, the reaction between MgB 4 and Mg was thermodynamically intensified leading to the formation of larger MgB 2 weight fraction as estimated from X‐ray diffraction (XRD) data using the Rietveld method. Despite no further improvement to the weight fraction of this phase by increasing the excess nominal Mg, it was shown that the critical current density ( J c ) was enhanced by almost one order of magnitude. At 5 K, 2 T, J c for the sample Mg 1.5 B 2 is estimated to be 4.5 × 10 5 A cm −2 . The enhancement of J c is attributed to the collective effect of improved grain connectivity and flux pinning by unreacted Mg. Incorporation of nano‐SiC for reaction resulted in a more gradual drop of J c with applied magnetic field. Hence, J c can be tailored to meet the range of fields intended for various applications via optimization of excess nominal Mg and dopant additions.