The effect of Ni doping on the electrical and magnetic properties of Y1-xNixBa2Cu3O7-δ delta superconductors

The Y1-xNixBa2Cu3O7-delta superconducting samples with low level of Ni concentration were prepared by the standard solid-state reaction. The AC susceptibility, magnetoresistivity, microstructure and the critical current density, J(c), of samples as a function of temperature, magnetic field and Ni doping are investigated. The AC susceptibility measurements show that the displacement of the peak temperature T-p of the imaginary part of the susceptibility chi '' versus magnetic field was reduced strongly by Ni doping up to an optimum level, which shows the increasing of flux pinning by Ni doping. The J(c) of samples was derived from AC susceptibility utilizing the Bean model. It shows an increasing in J(c) by Ni doping, at any temperature or magnetic field, consistent with the results of J(c) measurements. The magnetoresistance measurements were carried out under magnetic fields up to 1 T and explained by TAFC model. Utilizing this model, the vortex dynamic behaviour and the activation energy U (H) of the compound are investigated. We found that the U (H) increases and the resistive broadening is strongly reduced by Ni doping. The SEM measurements show that the grain sizes are clearly increased and the grain connections are improved by Ni doping. The results of all the observations taken from different measurements are consistent together and indicate the Ni doping has an effective role to improve the intergranular coupling and flux pinning.