Superconductor YBa₂Cu_3−xNi_xO_7−δ compounds prepared by electrospinning

This work describes the synthesis and characterization of (0.00 ≤ x ≤ 0.04) compounds prepared by an electrospinning technique. Stoichiometric solutions of Y-Ba-Cu-Ni were used to electrospin nanowires of these compounds, which were dried and heat-treated at temperatures ranging from 350 °C to 925 °C in an oxygen atmosphere. All samples were characterized by x-ray diffraction (XRD), scanning electron microscopy, and temperature magnetization curves. As prepared and dried at 100 °C, these samples present a nanowire shape with a smooth surface, with external diameters of ∼600 nm and a large length (>10 μm). After the heat treatment at 780 °C, all of them maintain their nanowire morphology with a rough surface with external diameters of ∼600 nm and length values ranging from 5 to 10 μm. All samples crystallize into the perovskite structure with orthorhombic symmetry (Pmmm space group). The most intense Bragg reflections arise from the phase and low-intensity peaks of additional phases. The temperature dependence of magnetization of these nanowires reveals a diamagnetic transition at temperatures close to the critical temperature, Tc, which is related to the superconductor transition in these compounds. The Tc values range between 70 and 93.2 K for samples with x = 0.04 to x = 0.00, respectively, where the substitution of Cu with Ni results in a lower Tc.