An improvement of the superconducting properties of bulk samples, by sintering at ambient pressure using radio-frequency induction heating, was reported. It was found that the TC(R = 0) transition temperature of the sintered sample was increased to ~40.00K as compared to the TC(R = 0) of ~25K for non-sintered MgB2 samples. A high critical current density of ~5.45 x 104A/cm2 (20K) was achieved for a sintered MgB2 sample whereas, for a non-sintered sample, JC was found to be ~1.20 x 103A/cm2 (20K). Detailed microstructural investigations by transmission electron microscopy revealed that most of the intergrain interfaces corresponded to low-angle grain boundaries. Based upon transmission electron microscopic explorations, these boundaries were recognized to be predominantly low-angle tilt boundaries. Surface microstructural features of the MgB2 sample as investigated by scanning electron microscopy revealed a well-connected uniform grain structure for the sintered samples.

Improved Superconducting Properties of MgB2 Bulk Materials Prepared by Sintering. A.Asthana, C.Shekhar, R.Giri, O.N.Srivastava: Journal of Physics D, 2003, 36, 2165-9