Effect of Ball-Milling Time on the Characterization and Physical Properties of Sintering YBa2Cu3O7−δ Phase

YBa2Cu3O7−δ superconducting samples were synthesized at different ball-milling times, 0≤t≤180 min, through the solid-state reaction technique. A comparison between the samples prepared by hand grinding and those prepared by high-speed ball-milling was studied. The variation of relative volume fraction, the lattice parameters, and the average crystallite size with t were examined using X-ray powder diffraction (XRD). The result is that the relative volume fraction of Y-123 phase increases by increasing t up to 15 min, and then it decreases with further increase in t. Moreover, the average crystallite size decreases as t increases from 0 to 60 min and then it increases with further increase in t. In addition, the surface morphology was studied through both scanning and transmission electron microscopes (SEM and TEM). Small crystallite grains, ranging from 25 to 70 nm, were detected between the matrices of Y-123 superconducting phase. The electrical resistivity and transport critical current density for Y-123 samples with different ball-milling time were measured by standard dc four-probe method. The superconducting transition temperature T c and the transport critical current density J c considerably enhance by increasing t to 15 and 30 min, respectively, beyond which they decrease. The suppression in both T c and J c may be due to decrease in relative volume fraction or degradation of the crystallite Y-123 matrix, causing increase in grain boundaries resistance. The Vickers microhardness for the prepared samples was measured, and the results indicate that the Vickers microhardness number H v increases as the ball-milling time increases.