Spark plasma sintered MgB2 co-added with c-BN and C60

Abstract

High density (above 92%) superconducting bulks of MgB2 co-added with cubic BN (c-BN) and fullerenes (C60) were obtained by the ex-situ spark plasma sintering (SPS). Compositions were (MgB2)(1−x)(C)x(c-BN)0.01, x = 0.0125, 0.025, 0.05, 0.075. The co-added sample (MgB2)0.975(C)0.025(c-BN)0.01 shows a marginally higher critical current density Jc at intermediate magnetic fields and below 15 K than for optimum samples added with c-BN or C60. For this sample, pinning is in the point pinning limit and the δTc mechanism is dominant. At high magnetic fields co-added samples are inferior to samples added with one additive, but are superior to pristine sample. Co-addition of c-BN and C60 is not effective for vortex pinning when compared with individual addition. The result is discussed based on phase formation aspects, microstructural details and residual strain. It was found that in the presence of C60, c-BN consumption with formation of MgNB9 is intensified with implications on different elements that influence pinning.