Effects of Ball Milling on the Sintering Process and Superconducting Properties of $(\hbox {MgB}_{2})_{0.96}\hbox {Ni}_{0.04}$ Bulks

Samples of (MgB₂)_0.96Ni_0.04 prepared by mechanical alloying were sintered at 750°C for 30 min. The reactive process and generating temperature of the second phase were investigated by employing differential thermal analysis, X-ray diffraction, and scanning electronic microscopy. Corresponding microstructures and superconducting properties have also been analyzed. It is found that two-step milling is effective in refining the structure and in eliminating flux jumps, although the corresponding J_c is slightly lowered due to the existence of excessive MgO. This observation indicates that the bulk samples prepared by two-step milling possess stable properties of magnetism and heat compared with the sample prepared by manual milling.