Superconducting properties of polycrystalline YBa_2Cu_3O_(7-d) prepared by sintering of ball-milled precursor powder

摘要

The effect of ball milling on the superconducting properties of polycrystalline YBa_2Cu_3O_y compounds has ben studied. The samples were synthesized by a solid state reaction by considering a thermal cycle with two stages of sintering at 950℃separated by intermediate crushing;;a traditional crushing (in a mortar) and another energetic (in a planetary crusher). The correlations between milling parameters, microstructure and superconducting properties have been investigated. The samples were characterized by X-ray diffraction, energy dispersive spectrometry and scanning electron microscopy. The critical current density of the samples was examined using current-voltage, ac-susceptibility and magnetization measurements. The temperature dependence of the resistivity under magnetic field has been studied to evaluate the upper critical and the irreversibility magnetic fields of these samples. It is demonstrated that ball milling is an effective approach for obtaining fine particles with size about 15 nm gathered into coral-like agglomerates and embedded in the matrix. Such decorated finer structure contributes to the enhancement of the inter-grains and intra-grains critical current density of the material under an applied magnetic field.