Papers by Keyword: Bi-2212

Abstract: The effect of La substitution on the structure and its modulation in samples with a nominal composition of Bi₂Sr_2-xLa_xCaCu₂O_8+d where 0≤x≤0.3 superconducting phase was investigated. The X-ray powder diffraction (XRPD) results showed an almost pure Bi-2212 phase, confirmed by the estimated amount of element concentration using dispersive energy X-ray spectroscopy (EDX). Scanning electron microscopy (SEM) micrographs showed a decrease of both crystallite size and connectivity when Lanthanum concentration increases. Le Bail refinement using the Jana2006 program gives a very good value of goodness of fit (GOF) factor. Also, the refinement reveals that for x=0.3 the orthorhombic cell transforms to the tetragonal one and the modulation vector q increases when increasing La concentration.

Abstract: Formation of bismuth-based high-T_c superconducting ceramics 2212 and 2223 with partial replacement of Bi by p-elements of group III (Ga, In, Tl), IV (Ge, Sn, Pb), or V (Sb) was studied. XRPD, DTA/TG, SEM/EDX, SQUID, and VSM were used for phase identification, structural analysis, grain morphology studies, chemical analysis and magnetic measurements.

Abstract: It is necessary to formpinning centers in superconductors to allow the flow of large currents throughthe specimens. To clarify the properties of pinning centers, it is preferableto investigate single crystals. In this study, heat treatment was used to dopevarious oxides into Bi₂Sr₂CaCu₂O_x(Bi-2212) single crystals prepared by self-flux methods and the criticalcurrent (Ic) was measured. The oxides used in this study were Al₂O₃and the rare earth oxides Er₂O₃and Nd₂O₃. At 77K, Nd₂O₃and Er₂O₃ are magnetic, whereas Al₂O₃is nonmagnetic. The Ic of the samples were measured as a current per width of 1cm (Ics). The resulting Ics of the Bi-2212 single crystal was 2.8A/cm and thatof the Al₂O₃ doped Bi-2212 sample was 4.5A/cm. Comparedwith these samples, doping the other rare earth oxides gave Ics values inexcess 10A/cm. The results indicated that the doping oxides were effective inoperating as pinning centers in the samples. We assumed the current path in asingle crystal, and calculated the Ics by superconducting current simulation.The results indicated that the oxides permeated from a crystal surface in aporous shape. The oxides increase the current which flow in the Cu-O₂planes that are parallel to the a-b plane.

Abstract: In the last years oxide materials for electronics show significant progress. However, many details regarding technology control of the properties have to be solved. For electronics, thin films and heterestructures are important taking advantage of integration and synergetic concepts leading to new types of devices and functionalities. It is notable that, while fabrication of new devices and materials showing new phenomena are booming, the growth principles and concepts are somehow developing slowly within this general trend. This is because in many cases, growth of materials is very personalized. Understanding of the bi-directional relationship between the general and particular principles deserves attention. The immediate benefit is that knowledge on growth for one material can be transferred to another one. In our work we have analyzed such relationships for some oxide multicomponent perovskites. Materials used in our examples are Bi-Sr-Ca-Cu-O and YBa₂Cu₃O₇, (Ca, Sr)CuO₂, (Ca, Ba)CuO₂ and Bi₄Ti₃O₁₂. Presented thin films or heterostructures are with c-axis and non-c-axis orientations and based on these examples we discuss some of the growth principles.

Abstract: Bi-2212 superconducting phase was synthesized via sol-gel method, and the experimental parameters such as the concentration of precursor solution and heat treatment temperature were adjusted to find the optimal conditions. Metal nitrates were adopted as the starting materials and ethylenediaminetetracetic acid (EDTA) as chelating agent. Precursor solutions and gel with different concentration were obtained through the addition of different content of distilled water as solvent followed by heating at certain temperature to form grey powders. Afterwards, the powders were sintered at different temperature for 10 hours, respectively. X-ray diffraction (XRD) was adopted to investigate the phase purity and crystallinity of the sample derived. Results reveal that the optimized precursor solution concentration is 27% and the optimized sintering temperature is 850°C.

Abstract: We fabricated Bi-2212/SrSO4 composite superconductors by the melt casting process and evaluated the effects of the powder mixing method and melting temperature on their microstructure and superconducting properties. In the melt casting process, the Bi-2212 powders were mixed with SrSO4 by hand-mixing (HM) and planetary ball milling (PBM) and then the powder mixtures were melted at 1100°C~1200°C, solidified, and annealed. We found that the powder mixture prepared by PBM was finer and more homogeneously mixed than that prepared by HM, resulting in more homogeneous microstructure and smaller SrSO4 and second phases after annealing. The critical current (Ic) also varied significantly with the powder mixing method and the melting temperature. The Ic of the annealed rod prepared by PBM was 193 A at 77 K when melted at 1100°C, which is higher than that of the annealed rod prepared by HM (132 A). This enhancement in the Ic value for the former is considered to be due to its more uniform microstructure.

Abstract: Vitreous cylinders with compositions Bi2-xPbxSr2CaCu2Oy, (x = 0 and 0.4) were prepared and used as precursors to fabricate textured bars through a Laser Floating Zone melting method (LFZ). The resulting textured cylindrical bars were annealed and were mechanically characterized through mechanical strength, σ, Young modulus, E, Vickers hardness, H, and Weibull parameters, S0 and m. The study of the mechanisms controlling the fracture process was made by means of the fractographical analysis using Laser Scanning Confocal Microscopy (LSCM). Finally, the microstructure was determined and correlated with the mechanical properties.