Polycrystalline YBa ₂ Cu ₃ O _7-δ with nano-sized Al ₂ O ₃ inclusions

Series of (YBa ₂ Cu ₃ O _7-δ ) _1-x (Al ₂ O ₃ ) _x samples have been prepared using solid state reaction method. Various amount of nano-sized Al ₂ O ₃ particles (∼50 nm) were added with (x=0, 0.005, 0.01, 0.02, and 0.05). The microstructure and the morphology of the polycrystalline samples have been characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM). The magneto-transport properties of these samples were investigated using resistance-temperature (R-T) and current-voltage (I-V) characteristics. All samples showed an orthorhombic structure with a tendency to transformation to tetragonal phase at higher levels of nanoparticles addition. The morphology of the surface of pure samples reveals a considerable number of weak-links, randomly oriented and clean grain boundaries. While in samples with nano inclusions, grain boundaries were filled with nanosized particle and have less number of weak-links. Significant enhancement of the superconducting critical current density J _c in applied magnetic field was observed due to nano Al ₂ O ₃ inclusions. However, further increase in the value of x decreases the transition temperature T _c and the critical current density J _c . These results were interpreted in terms of the flux pinning mechanisms in granular superconducting networks which leads to a better basic understanding of the performance of YBCO system in high applied magnetic fields.