MgB2 bulks were produced by in situ solid-state reaction in Ar gas using high-purity commercial powders of Mg metal and amorphous nano-B mixed in a fixed ratio of Mg:B = 1:2. Single-phase materials have been obtained and grain structure and its implications are reported. All samples were sintered at 775 °C for 3 h in Ar atmosphere. X-ray diffraction results show that high-purity MgB2 phase has been fabricated, which as well is reflected in critical temperature (Tc = 37.8 K). Magnetic measurements reveal a high critical current density (Jc) value such as 408 kA/cm2 when nano-amorphous boron is used. SEM studies show that nano-ordered MgB2 grains are formed, thereby creating large number of grain boundaries responsible for high critical current densities. Analysis of normalized pinning force curve as a function of reduced magnetic field indicates that dominant pinning is caused by grain boundaries.
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