Variation of the enhancement mechanism in the critical current density of Cu-doped MgB2 samples sintered at different temperatures

MgB2 samples with 3 at. % Cu addition were synthesized by means of in situ sintering at different temperatures (525, 575, and 850 degrees C). Based on thermal analysis, phase identification, and microstructural observation, it is first found that the Cu addition mainly concentrates at the edge of the void in the form of Mg2Cu and thus does not degrade the grain coupling of MgB2 phase in the low-temperature sintered sample. As sintering temperature rises to 850 degrees C, the MgB2 grains grow larger and some Cu addition may form MgCu2 nanoinclusions distributing in the MgB2 grains through the reaction, 2Mg(2)Cu((L))+6B = 3MgB(2) + MgCu2. As a result, the mechanism of enhancement in the J(c) of the Cu-doped MgB2 samples varies distinctly from the grain-boundary pinning to the possible MgCu2 nanoinclusions pinning as the sintering temperature increases from low temperature to high-temperature. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2982088]