Model for the low-temperature transport of Bi-based high-temperature superconducting tapes

Microstructure and Superconducting Properties of Bi-2223 Synthesized via Co-Precipitation Method: Effects of Graphene Nanoparticle Addition

The effects of graphene addition on the phase formation and superconducting properties of (Bi1.6Pb0.4)Sr2Ca2Cu3O10 (Bi-2223) ceramics synthesized using the co-precipitation method were systematically investigated. Series samples of Bi-2223 were added with different weight percentages (x = 0.0, 0.3, 0.5 and 1.0 wt.%) of graphene nanoparticles. The samples' phase formations and crystal structures were characterized via X-ray diffraction (XRD), while the superconducting critical temperatures, Tc, were investigated using alternating current susceptibility (ACS). The XRD showed that a high-Tc phase, Bi-2223, and a small low-Tc phase, Bi-2212, dominated the samples. The volume fraction of the Bi-2223 phase increased for the sample with x = 0.3 wt.% and 0.5 wt.% of graphene and slightly reduced at x = 1.0 wt.%. The ACS showed that the onset critical temperature, Tc-onset, phase lock-in temperature, Tcj, and coupling peak temperature, TP, decreased when graphene was added to the samples. The susceptibility-temperature (χ'-T) and (χ″-T) curves of each sample, where χ' and χ″ are the real and imaginary parts of the susceptibility, respectively, were obtained. The critical temperature of the pure sample was also measured.

Structural and functional modifications induced by X-ray nanopatterning in Bi-2212 single crystals

X-ray nanopatterning induces both mosaicity increase and oxygen depletion in the high-T_c superconductor Bi₂Sr₂CaCu₂O_8+δ.

Comparison of growth texture in round Bi2212 and flat Bi2223 wires and its relation to high critical current density development

Why Bi(2)Sr(2)CaCu(2)Ox (Bi2212) allows high critical current density Jc in round wires rather than only in the anisotropic tape form demanded by all other high temperature superconductors is important for future magnet applications. Here we compare the local texture of state-of-the-art Bi2212 and Bi2223 ((Bi,Pb)(2)Sr(2)Ca(2)Cu(3)O(10)), finding that round wire Bi2212 generates a dominant a-axis growth texture that also enforces a local biaxial texture (FWHM <15°) while simultaneously allowing the c-axes of its polycrystals to rotate azimuthally along and about the filament axis so as to generate macroscopically isotropic behavior. By contrast Bi2223 shows only a uniaxial (FWHM <15°) c-axis texture perpendicular to the tape plane without any in-plane texture. Consistent with these observations, a marked, field-increasing, field-decreasing J(c)(H) hysteresis characteristic of weak-linked systems appears in Bi2223 but is absent in Bi2212 round wire. Growth-induced texture on cooling from the melt step of the Bi2212 J(c) optimization process appears to be the key step in generating this highly desirable microstructure.

Crystal structure, chemical composition, and extended defects of the high-Tc (Bi,Pb)2Sr2Ca(n)-1CunO4 + 2n + delta compounds

This paper summarizes results obtained by high-resolution transmission electron microscopy on the crystal structure and microstructure of the (Bi,Pb)2Sr2Ca(n)-1CunO4 + 2n + delta high-Tc superconducting oxides. The experimental basis for the work presented here are high-resolution structure images obtained at ultra-thin (3 nm) areas of carefully prepared transmission electron microscope (TEM) samples. The analysis was carried out on a 400 kV TEM equipped with a pole piece yielding 0.17 nm point-to-point resolution. From the images obtained the projected crystal potential of the cations can be extracted directly, as confirmed by detailed image simulation. Structural analysis of the oxygen sublattice remains an unsolved problem by high-resolution TEM (HRTEM), mainly because of the small scattering factors, and thus the contribution of the oxygen sublattice to the image contrast is small. The (BiPb)2Sr2Ca(n)-1CunO4 + 2n + delta phases are modulated structures that can be understood as an average structure plus a superimposed displacement field. The crystal structure consists of BiO double layers and perovskite-type cuboids (containing Sr, Ca, Cu, and O), which are sandwiched between the BiO double layers. The displacement field can be directly analyzed by HRTEM, and the largest displacement amplitudes of 70 pm were determined for the Bi atoms in the n = 1 compound. The chemical composition of the n = 2 and n = 3 compounds was determined by EDX in the TEM for the cation sublattice. A significant (Ca + Sr) deficiency (approximately 10%) with respect to Cu was found. The (Sr + Ca)/Cu mole fraction ratio was 1.31 for the Bi-2212 phase and 1.14 for the Bi(Pb)-2223 phase. The oxygen content cannot be determined by EDX in the TEM with the accuracy necessary for a correlation with electrical and superconducting properties. The defect structure present in these materials, that is, intergrown lamellae with different crystal structures and equal or different chemical compositions, stacking faults, and grain boundaries, is summarized. The importance of grain boundaries for understanding and improving superconducting properties is emphasized.