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The critical current density versus temperature graph for the Bi 1 . 7 Pb 0 . 35 Sr 1 . 9 Ca 2 . 1 Cu 3 O x
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Bi1.7Pb0.35Sr1.9Ca2.1Cu 3Ox samples prepared by the classical method were studied by the AC magnetic susceptibility (χ = χ′ + iχ″) method. The annealing of the sample was concluded under different cooling rate conditions. The intergranular critical current densities and critical temperatures, estimated from the temperature dependence of the AC susc...
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... Fig. 2 gives information about the grain sizes and grain boundary effect for a given magnetic field strength. As seen from Fig. 2(a), the shielding effect is more noticeable for the 100 ◦ C/h cooling rate than for that of the 50 ◦ C/h and 25 ◦ C/h cooling rates for 150 A/m. Similar behaviour is seen for Fig. 2(b). The imaginary and real parts of the susceptibility shift to lower temperatures for a slow cooled sample for any magnetic field strength. Fig. 3 shows the Cole-Cole plots of the first harmonics of the samples with different cooling rates at H a = 40 A/m and f = 330 Hz. The volume fraction of grains, f g , for each sample (see Table I) can be estimated from the graph. Chen et al. [14] used the critical state model of Kim et al. [15] to calculate the AC susceptibility and determine the volume fraction of the grains for Bi(Pb)SrCaCuO superconductors. The determined f g value was used by Celebi [4] to calculate the matrix susceptibility. As seen from the graph, the Cole-Cole plots show dome shaped curves. The occupied area under the χ ( χ ) curve for the sample with 100 ◦ C/h cooling rate at 40 A/m is less than that of the samples with 25 ◦ C/h and 50 ◦ C/h cooling rates. Fig. 4 exhibits the critical current density versus temperature for the samples with 25 ◦ C/h, 50 ◦ C/h, and 100 ◦ C/h cooling rates. As seen from the graph, the critical ...
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... This J c is similar in magnitude to the ones reported for other polycrystalline cuprate superconductors [31,32]. We have included in the last paragraph of the introduction the following Motivation statement: ...
... The intergrain critical current density at the peak temperature J c (T p ) was between 17 and 22 A cm -2 for all samples. This J c is similar in magnitude to the ones reported for other polycrystalline cuprate superconductors [31,32]. ...
The effects of rare-earth elements M = Gd, Er, and La and alkali metals M = K, Li, Na, and Rb substitutions on Tl0.7M0.3Sr2Ca0.8Cr0.2Cu2O7 (Tl-1212) were investigated. The characterization includes X-ray diffraction method, scanning electron microscopy, electrical resistance and AC susceptibility measurements. X-ray diffraction patterns showed that almost all samples consisted of major Tl-1212 and minor Tl-1201 and Ca0.3Sr0.7CuO2 phase. Rare-earth elemental substitution improved the formation of the Tl-1212 phase but suppressed the transition temperature. Scanning electron micrographs showed smaller grain size in the substituted samples compared with non-substituted sample. The temperature-dependent electrical resistance measurements showed metallic normal state behavior for all samples. Alkali metals substitutions showed higher zero transition temperature, Tc-zero compared with the rare-earth elemental substitution. AC susceptibility measurements showed a higher superconducting transition, Tcχ′ for alkali metals substitutions (84–93 K) compared with the rare-earth elemental substitutions (50–61 K). The inter-grain critical current density at the peak temperature Tp of the imaginary part χ” Jc(Tp) measured using the Bean's model was between 17 and 22 A cm⁻². The effects of rare-earth elements and alkali metals substitutions were discussed in terms of ionic radius and the concept of average Cu valence.
The Bi-2223 (110K) phase high Tc superconductors were synthesized by conventional melt quenching technique. The nominal composition of the (110K) phase was (Bi1.6Pb0.4)Sr2Ca2Cu 3O10+dδ which was prepared from powders of Bi 2O3, PbO, SrCO3, CaCO3 and CuO having 99.99% purity. The synthesized precursors were quenched from 1200°C, 1250°C and 1300°C to room temperature and sandwiched between brass, stainless steel, copper and bronze blocks. These samples were analyzed by X-ray diffraction (XRD), DC electrical resistivity, scanning electron microscopy (SEM), EDS and density measurements. Lattice constants of the material were determined by indexing the diffraction peaks. Major phase is high-Tc 2223 phase with small percentage of 2212 phase. The highest volume fraction of 2223 phase is obtained for sample quenched on brass from 1250°C. The SEM results indicate that 2223 phase may have been formed and the long grains of this phase might be obtained by quenching at this temperature. The atomic distribution ratio of each component element on the surface of the sample was investigated by EDS. The change in structural and electrical parameters could be ascribed to the oxygen diffusion behavior, resulting in hole carrier concentration.
The influence of partial substitution of Ca by La on (Bi,Pb)2223 phase purity and intergranular dissipative processes is characterized by XRD and a.c.magnetic susceptibility function of temperature and a.c. field amplitude. The intergranular phase diagram Hp function of temperature and the intragrain contributions of effective volume fraction of the grains f g were estimed.
We have investigated the effect of addition of Gd in Bi1.8Pb0.35Sr1.9Ca2.1Cu3GdxOy superconductor with x=0, 0.1, 0.2, 0.3, 0.4 and 0.5. The samples were prepared by standard solid-state reaction methods. The investigation consisted of X-ray diffraction (XRD), scanning electron microscopy (SEM), dc electrical resistivity, hole concentration and transport critical current density measurements. Transport measurements indicated that the superconducting transition temperature, transport critical current density and hole concentration values of the samples strongly depend on the Gd addition. The values of Tc, and Jc of the samples decreased with the increase in Gd addition. When Gd addition ratio was increased, surface morphology and grain connectivity of the samples were observed to degrade from SEM investigations and phase ratio of the high-Tc (Bi-2223) phase to the low-Tc (Bi-2212) phase decreased (XRD measurements). The possible reasons for the observed degradation in superconducting and microstructure properties of Bi-2223 due to Gd addition were discussed.
We have investigated the effect of the cooling rates in the Bi-2223 superconducting samples prepared by standard solid-state reaction method using electrical resistivity, transport critical current density, and XRD (X-ray diffraction) measurements. We estimated the transition temperature values from the DC resistivity measurements. We observed that transition temperature, Tc, and transport critical current density, , depend on the cooling rates of the samples. They both increase with increasing cooling rates. We estimated the peak temperature, Tp, from our previous ac susceptibility measurements. The pinning force density increased with increasing the cooling rate. XRD patterns are used to calculate lattice parameter c and obtain information about Bi-2223 phase ratio.
