Magnetoresistance Study of Y3Ba5Cu8O18 Superconducting Phase Substituted by Nd3+ and Ca2+ Ions

Superconducting samples of type Y_3?x Nd _x Ba_5?x Ca _x Cu₈O₁₈ with 0.0 ≤ x ≤ 0.4 have been prepared via the solid-state reaction technique. The prepared samples were characterized using X-ray powder diffraction (XRD) technique for phase analysis. The elemental content of the prepared samples was determined using particle-induced X-ray emission (PIXE). In addition, the oxygen content of these samples was obtained using non-Rutherford backscattering spectroscopy (RBS) at 3 MeV proton beam. The results indicate that these substitutions do not affect the orthorhombic structure, while they decrease the oxygen content of Y-358 phase. The electrical resistivity of the prepared samples was measured by the conventional four-probe technique from room temperature down to the zero superconducting transition temperature (T ₀). A slight change in the superconducting transition temperature (T _c) is observed for 0 ≤ x ≤ 0.1, and then it decreases linearly with further increase in x. The linear decrease in T _c is attributed mainly to the partial substitution of Ba²⁺ ions by Ca²⁺ ions rather than the partial substitution of Y³⁺ ions by Nd³⁺ ions. The effect of magnetic fields up to 4.44 kG on the electrical resistivity has been studied to investigate the vortex dynamics for the prepared samples. The experimental data, in the second stage of superconducting transition, fit well with the thermally activated flux creep (TAFC) model, and the activation energy U(B) shows a power law dependence on magnetic field as B ^?β . Also, the transition width is related to the magnetic field according to the relation ΔT α B ⁿ . The values of β and n are strongly dependent on the Nd³⁺ and Ca²⁺ ion substitution. The magnetic field and temperature dependence of the activation energy U(B, T) is found to be U(B, T)? ΔT B ^?η , where η = β + n. Furthermore, the critical current density at zero temperature, J _c(0), as a function of the applied field was calculated for all the prepared samples. The result shows an enhancement in J _c(0) of Y-358 phase at x equals 0.4 at different applied fields.