Effect of Yb Substitution in Bi_(1.6)Pb_(0.4)Sr_2Ca_(2-x)Yb_xCu_3O_y Superconductor

摘要

This paper reports on the results of Yb substitution for Ca on the superconductivity and structural properties of Bi_(1.6)Pb_(0.4)Sr_2Ca_(2-x)Yb_xCu_3O_y superconducting samples with x = 0.000, 0.025, 0.050, 0.100 and 0.200 which prepared by coprecipitation (COP) method. The samples were characterized by X-ray diffraction (XRD), field-emission scanning electron (FESEM), electrical and resistivity measurement by four-probe method. It was found that the substitution of Yb decreased the critical temperature (T_(c zero)), critical current density (J_c) and volume fraction of Bi-2223 phase. The samples have T_(c zero) in the range 77 to 100 K. T_(c zero) gradually decreased with an increase in Yb concentration, corresponding to small change of the carrier concentration. J_c was measured to be 5.7512 A/cm~2 for pure sample and decreased to 4.1910 A/cm~2 for x = 0.025 at 77 K. The crystallographic structure was found to change slightly from tetragonal to orthorhombic in Yb substituted samples. The lattice parameter c of Yb samples decreased due to the incorporation of Yb~(3+) (0.858 A) with smaller ionic size compare to Ca~(2+) (0.99 A). From the SEM observation, the grain connectivity became weak with smaller plate-like grain for x＞0.025 Yb concentration resulting in the decreased of J_c.