Effects of Dy₂O₃ nanoparticles on intergranular coupling and excess conductivity of low porous YBa₂Cu₃O_7−δ superconductor ceramic

Abstract

The incorporation of foreign nanostructure oxide phase into the ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7-d}$ ($Y123$) superconductor material is capable of producing trapping sites and upgrading the property of flux pinning (FP). Bulk ceramics with porosity around 19% ± 1% having a nominal composition $Y123+{x\mathrm{ Dy}}_{2}{\mathrm{O}}_{3}$ are prepared via the solid-state reaction method. ${\mathrm{Dy}}_{2}{\mathrm{O}}_{3}$ nanoparticles (${\mathrm{Dy}}_{2}{\mathrm{O}}_{3}$-$\mathrm{NPs}$) with an average size of about 20 nm and content x = 0.0, 0.1, 0.2, and 0.5 wt% are considered in this study. The structure, microstructure, magnetic susceptibility, electrical properties, and fluctuation-induced conductivity were investigated in detail. The X-ray diffraction (XRD) patterns showed the existence of ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7-d}$ with orthorhombic structure as a major phase. The microstructural examination using scanning electron microscope (SEM) and energy-dispersive X-ray (EDX) spectroscopy showed that $Dy$-rich nano-agglomeration segregated at the grain boundaries or on the surface of Y123 grains. The volume fraction of superconductor grain (${f}_{\mathrm{sg}}$) and Josephson energy coupling $({\text{E}}_{j})$ were extracted from AC susceptibility versus temperature measurements. From log–log plots of the excess conductivity versus, the reduced temperature and using the Aslamazov–Larkin model, we assessed the crossover temperatures between different regimes of conductivity, the effective thickness of the 2D layer system (d), the coherence length (${\xi }_{\mathrm{co}}$), the penetration depth (${\lambda }_{o}$), the critical current density (${J}_{\text{c }}(0)$) as well as the upper and the lower critical magnetic fields (${B}_{\text{c2}}(0)$ and (${B}_{\text{c1}}(0)$) at zero kelvin for all the ceramics. ${\xi }_{co}$ and ${\lambda }_{o}$ decreased, while ${J}_{\text{c }}(0)$, ${B}_{\text{c2}}(0)$, and ${B}_{\text{c1}}(0)$ increased with ${\mathrm{Dy}}_{2}{\mathrm{O}}_{3}$-NPs addition up to 0.2 wt% results in better flux trapping. The highest values of ${B}_{{\text{c}}{1}}(0)$, ${B}_{{\text{c}}{2}}(0)$, and ${J}_{\text{c}}(0)$ are found to be equal to 2.6 Tesla, 120.6 Tesla, and 65.64 × 10³ A/cm², respectively. The inclusion of a suitable amount of ${\mathrm{Dy}}_{2}{\mathrm{O}}_{3}$-NPs into the ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7-d}$ superconductor is an encouraging way for developing material with good superconducting performances for practical applications such as the second-generation HTS technologies for power transmission and fault current limiters.