Effect of pelletization pressure on the physical and mechanical properties of (Bi, Pb)-2223 superconductors

Abstract

Conventional solid-state reaction technique was used to prepare bulk samples with nominal composition of (Bi, Pb)2Sr2Ca2Cu3O10+δ superconductors. The prepared powder was pelletized at different pressure (P = 0.3, 0.7, 1.0, 1.4 and 1.9 GPa) before the calcination process. Structural parameters and phase purity were evaluated using x-ray diffraction (XRD). The formation of the tetragonal major phase is improved with increasing the pelletization pressure up to 1.4 GPa. The morphology and elemental compositions were performed by using scanning electron microscope (SEM) and energy dispersive x-ray spectroscopy (EDX), respectively. The results showed the enhancement of the grain alignment at an optimum pelletization pressure of 1.4 GPa with a decrease in the porosity percentages. Superconducting transition temperature (Tc) and the critical current density (Jc) were obtained by means of DC electrical resistivity and the voltage-current characteristic, respectively. Both Tc and Jc are improved with increase the pelletization pressure up to 1.4 GPa. Room temperature Vickers microhardness Hv measurement was performed at different applied loads (0.245-9.8 N) and times (10-60 s). As a result of the Hv measurements, all the prepared samples have a normal indentation size effect behaviour. It was found that P = 1.4 GPa was the optimal pressure to improve the microhardness in the (Bi, Pb)-2223 phase. The measured Hv data were theoretically analysed using Meyer's law, the Hays-Kendall approach, the elastic plastic deformation model and the proportional sample resistance. The last model was recognized to be the best theoretical one describing the true Hv values for the considered phase. Room temperature indentation creep analysis was also performed using time-dependent microhardness to identify the operative creep mechanisms in the measured samples.