Investigation of microhardness and superconducting parameters of CNTs blended YBCO superconductor

Here we report the effect of CNTs addition on the microhardness and superconducting properties of YBa2Cu3O7-delta (YBCO) high-temperature superconductor. All the composite samples exhibit orthorhombic structure, maintain single phase and to belong to P-mmm space group as evidence from the Rietveld refinement analysis. From FESEM micrographs, for all samples extended rods like structure is observed. The microhardness number (H-V) enhances non-linearly by application of load from 0 to 3 N, beyond which the curve reaches a saturation limit. As the microhardness number gradually increases under substitution of CNTs revealed that CNTs addition has resulted significant effect on microhardness property of the YBCO superconductor. Different models like Meyer's law, Hays-Kendall approach and elastic/plastic deformation model are utilized to examine the microhardness properties of the high-temperature superconductor. Finally proportional specimen resistance model is the most efficient model to describe the microhardness properties of CNTs doped YBCO samples. The superconducting transition temperature (T-C) is obtained from resistivity vs. temperature measurement and AC susceptibility measurement. From both the measurements, it is obvious that T-C enhances with CNTs addition up to 0.5 wt % and then decreases. For 0.5 wt % CNTs doped YBCO sample the value of T-C is nearly 96 K. As the addition of CNTs to the YBCO matrix creates artificial pinning centers inside the YBCO matrix and increases the superconducting volume fraction, hence the observed value of critical current density for all composite samples are more than that of pristine YBCO. The maximum value of J(c) is observed for 0.5 wt % sample and the value is 1.8 times more than that of pure YBCO. Utilizing Zeldov model the characteristics pinning potential energy for all composite samples is calculated and the response is very similar to that of critical current density under addition of CNTs.