Transport current density of (Bi1.6Pb0.4)Sr2Ca2Cu3O10 superconductor added with different nano-sized ZnO

The (Bi_1.6Pb_0.4)Sr₂Ca₂Cu₃O₁₀ZnO _x (x=0–0.05 wt%) superconductor with addition of ZnO with average particle size 6 nm and 30 nm was prepared using the co-precipitation method. The ZnO particle size was larger than the coherence length, ξ, and smaller than the penetration depth, λ, of the superconductor. The microstructure, transition temperature (T _c) and transport critical current density (J _c) were studied. SEM micrographs showed a homogeneous distribution of ZnO nanoparticles throughout the samples. J _c of all the ZnO added samples were higher than the non-ZnO added sample. The maximal J _c and T _c were observed when x=0.02 wt% for both series. J _c (77 K) of the 6-nm ZnO added sample was 46 times larger than the non-ZnO added sample. The 6-nm ZnO added sample also showed higher J _c compared to the 30-nm ZnO added sample. ZnO with size closer to ξ was more effective in enhancing J _c.     

Superconducting screen printed thick films of YBa2Cu3O7 and Bi1.6Pb0.4Sr1.6Ca2.4Cu3O10 on polycrystalline substrates

Thick films of YBa₂Cu₃O₇ and Bi_1.6Pb_0.4Sr_1.6Ca_2.4Cu₂O₁₀ have been prepared using a screen printing method on polycrystalline substrates. The films have been characterized by X-ray diffraction, electrical measurements and SEM observations. YBa₂Cu₃O₇ films exhibited T_c ranging from 80 to 87 K on Y₂BaCuO₅ substrates while Bi_1.6Pb_0.5Sr_1.6Ca_2.4Cu₃O₁₀ films on polycrystalline MgO reached the zero resistance state at 104 K with critical current densities of up to 10 A/cm² at 77 K.     

Critical addition of Ti to maintain the Tc of (Bi1-zTiz)1.6Pb0.4Sr2Ca2Cu3Ox above 100 K

Influence of Ti addition (substitution for Bi) on T_c is studied for high T_c (Bi_1-zTi_z)_1.6Pb_0.4Sr₂Ca₂Cu₃O_x. We found a critical Ti addition to keep high T_c (above 100 K) of the (Bi_1-zTi_z)_1.6Pb_0.4Sr₂Ca₂Cu₃O_x. The high-T_c phase can be found up to 0.5 of z. It is explained by an abnormal T_c change which is found from 0.3 to 0.5 of z. Based on results of the electrical resistivity and x-ray diffraction, an abnormal T_c change is discussed.     

Comparative photoemission study of Bi2(Sr,Ca)3Cu2O8+y and Bi1.7Pb0.3Sr2Ca2Cu3O10+y

The electronic structure of Bi-based 2223 single phase superconductor has been studied by ultraviolet and X-ray photoemission. By comparison with that of 2212 phase superconductor, we find a higher density of states nearE _F for 2223 phase. From analysis of the Cu 2p core-level spectroscopy, we obtain a relatively smaller charge transfer energy between copper and oxygen as well as the Coulomb repulsion energy on Cu site for 2223 phase. We relate these changes to the increase of hole concentration from 2212 to 2223 phase. The experimental results support the viewpoint that the transition temperature should be correlated with the density of states atE _F .     

Thermoelectromotive force in Bi2Sr2Ca2Cu4O11 bismuth-based high-temperature superconductor

The temperature dependence of the thermoemf in Bi₂Sr₂Ca₂Cu₄O₁₁ bismuth-based high-temperature superconductors is studied. The thermoemf is positive at high temperatures (T > 300 K) and negative at low temperatures. As the temperature decreases, the thermoemf reaches a maximum slightly above T _c and then sharply drops to zero. The results can be explained in the framework of the two-band theory with a linear temperature term.     

Electronic structure of the trilayer cuprate superconductor Bi(2)Sr(2)Ca(2)Cu(3)O(10+delta)

The low-energy electronic structure of the nearly optimally doped trilayer cuprate superconductor Bi(2)Sr(2)Ca(2)Cu(3)O(10+delta) is investigated by angle-resolved photoemission spectroscopy. The normal state quasiparticle dispersion and Fermi surface and the superconducting d-wave gap and coherence peak are observed and compared with those of single- and bilayer systems. We find that both the superconducting gap magnitude and the relative coherence-peak intensity scale linearly with T(c) for various optimally doped materials.     

Low-field irreversibility line and its anisotropy of textured (Bi,Pb)2Sr2Ca2Cu3Oy silver-clad tapes

The irreversibility line H_irr(T) of textured (Bi,Pb)₂Sr₂Ca₂Cu₃O_y silver-clad tapes was obtained by ac susceptibility (ACS) and magnetoresistivity (MR) below 1500 G. It is found that, in the framework of flux motion, the H_irr(T) is determined by the thermally activated flux flow (TAFF) rather than the so-called giant flux creep, and the experimentally obtained H_irr(T) line is related to a certain resistivity criterion in both ACS and resistivity measurements. H_irr(T) is found to be significantly depressed by the amplitude of applied driving AC field and generally lower than that measured from the resistivity. The anisotropy in H_irr(T) is found to follow a scaling behaviour as described by the anisotropic effective mass model.     

Weak link problem and intragrain current density in polycrystalline Bi1Ca1Sr1Cu2Ox and Tl2Ca2Ba2Cu3O10

Polycrystalline sintered specimen were investigated by means of ac susceptibility and inductive critical current measurements. Main objects are whether the new highT _c oxides have a weakly coupled intergranular structure and to get information about the intragrain critical current density. The Tl₂Ca₂Ba₂Cu₃O₁₀ specimen shows a connective nature similar to YBa₂Cu₃O₇ with low intergrain currents (100 A/cm² at 100K,B=0 T) and high intragrain ones (4.5·10⁵ A/cm² at 100K,B=0 T). The investigation of the Bi₁Ca₁Sr₁Cu₂O_x specimen becomes complex due to the presence of two superconducting phases and the low intragrain critical current density of the lowerT _c phase.     

Influence of heat treatment on the superconducting properties of Bi1.6Pb0.3Sb0.1Sr2Ca2Cu3O y

Differently heat-treated samples with the nominal composition Bi_1.6Pb_0.3Sb_0.1Sr₂Ca₂Cu₃O _y were studied by resistance and ac susceptibility measurements in the temperature range 77 K<T<200 K. The X-ray diffraction patterns at room temperature were also investigated. The experimental results show that repeated quenchings can depress the formation of the 80 K phase, and enhance the formation of the 110 K phase.     

Current-voltage characteristics of a foamed Bi1.8Pb0.3Sr2Ca2Cu3O x high-temperature superconductor with fractal cluster structure

The influence of the structure of foamed polycrystalline bismuth-based superconductors on their critical currents and current-voltage characteristics is studied. It is found that superconducting foams have a fractal structure, and the fractal dimension of the boundary between the normal and superconducting phases is estimated. The magnetic and transport properties of superconducting foams are investigated, and the current-voltage characteristics are obtained in a wide range of currents. The effect of percolation phenomena on vortex pinning in a foamed superconductor is considered. The current-voltage characteristics of the superconducting foams at the beginning of the resistive transition are found to be in good agreement with a model in which a magnetic flux is assumed to be trapped in the fractal clusters of a normal phase.