Partially-oriented MgB2 superconducting bulks with addition of B4C and cubic BN obtained by slip casting under high magnetic field and spark plasma sintering

Abstract

Partially-oriented MgB2 bulk discs (13 and 9 %) with the starting compositions of (MgB2)0.99(B4C)0.01 and (MgB2)0.99(c-BN)0.01 were fabricated by slip casting under an H0 = 12 T magnetic field (perpendicular to the disc surface) and subsequent spark plasma sintering. The maximum critical current density and irreversibility field are for H//H0 (H=applied field). These values are higher or similar to the randomly-oriented samples with the same composition. The maximum volume pinning force (Fp) is lower in the partially-oriented ones than in the randomly-oriented samples. The pinning-force-related parameters depend on the additive and orientation. Assessment of the major pinning mechanism within the scaling and percolation models considering these parameters shows significant limitations. A method to scale Fp is proposed; for the randomly and partially-oriented samples (that show an extra peak in Fp), the single and double Gaussian functions fit well. The results suggest an anisotropic influence of carbon substituting for boron in the MgB2.