Effects of La doping on the structure and superconducting properties of Bi-2212

A series of Bi2-xLaxSr2CaCu2O8+delta (x = 0.00, 0.05, 0.10, 0.15, and 0.20) ceramic samples were synthesized by co-precipitation (CP) method. In this work, the influence of La doping on the phase evolution, microstructure, critical transition temperature, and flux pinning properties of Bi-2212 was investigated. The results indicate that La doping significantly promotes the formation of the Bi-2212 phase. As the La content increases, the a and b axis lengths of Bi-2212 structure gradually increase, while the c-axis length decreases. The La doping will introduce compressive stress into the Bi-O layers. Meanwhile, the modulation structure in Bi-2212 becomes enhanced with La substitution by decreasing the modulation period, which is effectively explained by the extra oxygen model. Furthermore, the critical transition temperatures (Tconset\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$T_c<^>{onset}$$\end{document}) initially increases and then decreases with higher La doping levels, reaching a maximum Tconset\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$T_c<^>{onset}$$\end{document} of 85.9 K for the sample with x = 0.15. The sample also exhibits the strongest flux pinning capability.