Improved superconducting properties by La addition in (Bi,Pb)-2212 bulk superconductor

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• 作者：A. Biju ; K. Vinod ; R.P. Aloysius ; U. Syamaprasad
• 关键词：High T_C superconductor ; Solid state reaction ; Microstructure ; Electrical transport
• 刊名：Journal of Alloys and Compounds
• 出版年：2007
• 期刊代码：45_09258388
• 类别：ms
• 出版时间：4 April 2007
• 卷：431
• 期：1-2
• 页码：49-55
• 文件大小：1242 K

摘要

The effects of La addition on the structural and superconducting properties of (Bi,Pb)-2212 bulk superconductor prepared by solid state synthesis in the polycrystalline form were studied. The La content of the samples was varied from 0 to 0.5 on a general stoichiometry of Bi_1.7Pb_0.4Sr_2.0Ca_1.1Cu_2.1La_xO_y. Phase analysis by XRD, microstructural examination by SEM, measurements of density and superconducting properties were done to evaluate the relative performance of the samples. The critical temperature (T_C) and critical current density, in zero [J_C(0)] and applied field [J_C(H)], of La added samples were found to be much higher than those of the pure sample for optimum doping levels. A maximum T_C-onset of 93.5 K (x = 0.3) and a maximum J_C(0) of 676 A/cm² (x = 0.2) at 64 K were observed for the doped samples as against 76.7 K and 100.5 A/cm² at 64 K for the pure sample, respectively. At higher doping levels the T_C and J_C(0) decrease from the maximum values. The increase in T_C and J_C(0) and the improved J_C-H characteristics are explained to be due to the substitution of La³⁺ in place of Sr²⁺ with a consequent change in the carrier (hole) concentration in the Cu–O₂ planes, and to be due to the flux pinning effect of structural defects and nanoscale precipitates brought about by La addition.