Pinning enhancement in nano-SiC and Si3N4 doped MgB2 tapes: A comparative study

The effect of nanometer SiC and Si3N4 particles addition on the crystal structure and superconducting properties of MgB2 tapes was systemically studied. The a-axis of MgB2 lattice was shortened by nano-SiC addition due to the carbon substitution induced lattice distortion of the honeycomb boron sheet. By contrast, the a-axis parameter was slightly increased in nano-Si3N4 doped tapes, possibly because of a slight Si substitution for B site. The amount of Mg2Si phase was lower in nano-SiC doped tapes than in nano-Si3N4 doped ones with the same doping concentration of Si, suggesting that more Si might have entered the MgB2 matrix in the former. This can be treated as an indirect evidence for the co-substitution of Si and C for B in nano-SiC doped samples. Our comparative study reveals that the enhanced flux pinning in both nano-SiC and Si3N4 doped tapes should mainly originate from the in-plane lattice distortion due to the element-substitution on boron sheet.