Increase of critical current density with doping carbon nano-tubes in YBa2Cu3O7-δ

The effects of carbon nano-tubes (CNTs) on the crystal structure and superconducting properties of YBa2Cu3O7-delta (Y-123) compound were studied. Samples were synthesized using standard solid-state reaction technique by adding CNT up to 1 wt% and X-ray diffraction data confirm the single phase orthorhombic structure for all the samples. Current-voltage measurements in magnetic fields up to 9 T were used to study the pinning energy U-J and critical current density J(c) as a function of magnetic field at fixed temperature. We find that while T-c does not change much with the CNT doping (91-92 K), both U-J and J(c) increase systematically up to 0.7 wt% CNT doping in a broad magnetic field ranges between 0.1 and 9 T and J(c) in the 0.7 wt% CNT doped sample is at least 10 times larger than that of the pure Y-123. The scanning electron microscope image shows that CNTs are forming an electrical-network between grains. These observations suggest that the CNT addition to the Y-123-compounds improve the electrical connection between superconducting grains to result in the J(c) increase. (C) 2008 Elsevier B.V. All rights reserved.