Spark plasma sintering of MgB2 in the two-temperature route

Superconducting bulks of MgB2 were obtained by an ex-situ two-temperature route applied to spark plasma sintering (SPS). Processing of samples was performed at lower temperatures than previously reported. Samples produced by the two-temperature route show a higher morphological uniformity, a higher density (above 98%), a higher Vickers hardness, and undesirable stronger microscale flux jumps, as indicated by magnetic relaxation measurements when compared to a sample obtained by the one-temperature route (95.3% relative density). At the same time, all sintered samples show approximately constant crystallite size, critical current density, irreversibility field, critical temperature, weight fraction of impurity phases (MgB4 and MgO), and the amount of carbon accidentally introduced during SPS processing.

► MgB2 was obtained by ex-situ SPS in the two-temperature (A) route (98% density).
► Tc, Jc, Hirr are similar to a one-temperature (B) SPS sample (95.3% density).
► Crystallite size, amount of impurity phases, accidental O2 and C intake are similar.
► Sample A shows better morphological uniformity.
► A higher Vickers hardness and stronger microscale flux jumps are for sample A.