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−δ (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 UJ and critical current density Jc as a function of magnetic field at fixed temperature. We find that while Tc does not change much with the CNT doping (91–92 K), both UJ and Jc increase systematically up to 0.7 wt% CNT doping in a broad magnetic field ranges between 0.1 and 9 T and Jc 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 Jc increase.