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Abstract: The microstructure and electrical properties of the rare-earth Lu doped (Bi, Pb)-2212 superconductor have been investigated. The Lu concentration is varied from x =0.000 to 0.150 in a general stoichiometry of Bi1.6Pb0.5Sr2−x Lu x Ca1.1Cu2.1O8+δ . The X-ray diffractometer and energy dispersive X-ray spectroscopy analyses show that Lu atoms are successfully substituted into the (Bi, Pb)-2212 system and they induce significant changes in the microstructure, hole concentration, critical temperature, self- and in-field critical current density of the system. The flux pinning force (F P) calculated from the field dependant J C values shows that the irreversibility lines (IL) of the Lu substituted (Bi, Pb)-2212 shift towards higher fields to different extents depending on the Lu stoichiometry. The samples with x =0.100 show a maximum F P of 1395±1×103 Nm−3 as against 30±1×103 Nm−3 for the pure sample. The changes in hole concentration followed by very high enhancement of critical temperature (T C), self-field J C, J C(B) characteristics and F P due to Lu substitution are of great scientific and technological significance and the results are explained on the basis of microstructural variation with respect to Lu stoichiometry, hole optimization and formation of point defects due to the doping of Lu atoms in Bi1.6Pb0.5Sr2−x Lu x Ca1.1Cu2.1O8+δ system. [Copyright &y& Elsevier]

Abstract: The effect of substitution of rare-earth Lu on the glass transition temperature (T g), the temperature and magnetic field dependent activation energy [U 0(B,T)] and flux pinning properties of Bi1.6Pb0.5Sr2−x Lu x Ca1.1Cu2.1O8+δ superconductor was studied. A large broadening of resistive transition in magnetic field is observed which is a direct evidence for the thermal fluctuation in the vortex system and hence the modified vortex-glass to liquid transition theory is used to calculate the values of T g and U 0(B,T). The resistivity shows a glassy behavior even at higher temperatures and magnetic fields for the Lu stoichiometry x =0.100 which is believed to come mainly from the point defects arised due to the substitution of Lu atoms in the (Bi, Pb)-2212 system. The results also show that the values of T g, magnetic field dependent activation energy U 0(B) and U 0(B,T) are maximum for x =0.100, which shows that the flux lines are effectively pinned and the vortices are in glassy state for this sample. The enhancement in U 0(B,T) and the flux pinning properties of the (Bi, Pb)-2212 system due to Lu doping has both scientific and technological importance. Also, for temperatures below the superconducting transition temperature (T C), a scaling of all measured resistivity curves in magnetic field (B =0.4 and 0.8T) is obtained for each stoichiometry. This scaling obtained in the presence of magnetic field is quite useful for better understanding of the behavior of the vortex-liquid in high temperature superconductors. [Copyright &y& Elsevier]

Abstract: The resistivity of Bi1.6Pb0.5Sr2−x Eu x Ca1.1Cu2.1O8+δ (0.000≤ x ≤0.180) superconductor has been measured as a function of temperature and magnetic field. The resistivity shows a glassy behavior even at higher temperatures and magnetic fields for the Eu-doped samples as compared with the Eu free sample. The values of glass-transition temperature [T g], magnetic field dependent activation energy [U 0(B)] and the temperature and magnetic field dependent activation energy [U 0(B,T)] are found to be maximum for optimal doping levels (x =0.135) which shows that the flux lines are effectively pinned in this sample. Also for temperatures below the superconducting transition temperature (T C), a scaling of measured resistivity curves in magnetic field (B =0.4 and 0.8T) is obtained and this scaling is quite useful for better understanding of the behavior of the flux vortices in high temperature superconductors. [Copyright &y& Elsevier]

Abstract: The influence of sintering temperature on the microstructure and superconducting properties of Bi1.7Pb0.4Sr1.8Yb0.2Ca1.1Cu2.1O8+δ has been investigated. Yb-free (Bi1.7Pb0.4Sr2.0Ca1.1Cu2.1O8+δ ) and Yb-substituted (Bi1.7Pb0.4Sr1.8Yb0.2Ca1.1Cu2.1O8+δ ) superconducting samples are prepared by solid-state synthesis in bulk form. Significant variations in microstructure, critical current density (J C) and flux pinning properties have been observed for Yb-substituted samples, sintered at different temperatures in the range 846–852°C. The flux pinning force (F P) calculated from the field dependant J C values show that the irreversibility lines (ILs) of Yb-substituted samples shift towards higher fields to different extents depending on the sintering temperature. The samples sintered at 846°C show maximum flux pinning force of 896kNm−3 and the peak position of F P shifts to higher fields (0.92T) as against 16kNm−3 and 0.12T for the undoped sample sintered at 848°C. But the self-field J C value of the samples sintered at 846°C is lower than that of the samples sintered at 852°C, which show the maximum self-field J C due to improved microstructure. The variation in microstructure followed by very high enhancement of self-field J C, J C–B characteristic and pinning force density due to Yb substitution within a narrow temperature range is of great technological relevance. [Copyright &y& Elsevier]

Abstract: The influence of sintering temperature on microstructural and superconducting properties of Gd-substituted (Bi,Pb)-2212 superconductor was investigated. It is found that the microstructure of the system can be tailored and refined so as to yield the best superconducting properties in terms of critical current density (J C) and flux pinning by heat treating at a temperature in the range 846–860 °C. The samples sintered at 858 °C show the maximum self-field J C of 31,960 kA m− 2 and those sintered at 846 °C show the maximum flux pinning force [F P = 1698 kN m− 3] as against 1860 kA m− 2 and 16 kN m− 3, respectively for the undoped sample sintered at its optimum sintering temperature. The changes in microstructure followed by very high enhancement of J C, J C–B characteristics and F P due to Gd-substitution within a small temperature range, is of great scientific and technological significance. [Copyright &y& Elsevier]

Abstract: A systematic study on phase evolution, bulk density, resistivity, T C, J C, and J C–B characteristics of pure and Yb substituted (Bi,Pb)-2212 samples at different cationic sites (Bi, Ca, Sr) has been carried out. The results show that there is a substantial improvement in the overall superconducting properties, particularly the T C, J C, and J C–B characteristics of the Yb substituted samples. Further, it is observed that there is a significant shift in the peak value of the bulk pinning force density F pmax towards higher magnetic fields when Yb is substituted at different cationic sites, indicative of the enhanced flux pinning strength in these samples. All the substituted samples show almost identical microstructure, but are distinctly different from pure (Bi,Pb)-2212. The natural layered growth mechanism of (Bi,Pb)-2212 is disrupted by grain growth, and coarsening in random directions. The substituted Yb atoms enter into the corresponding sites in (Bi,Pb)-2212, which create inhomogeneities in the crystal structure, decrease the hole concentration, and may produce point like defects. These defects act as the pinning centers. There is also the possibility of formation of nanoscale secondary phases, which can act as pinning centers. [Copyright &y& Elsevier]

Abstract: Superconducting (Tl0.5Pb0.5)(Sr0.85Ba0.15)2Ca2Cu3O z films were prepared on highly polished, untextured silver substrates. A superconducting transition temperature (T c) of 114.9±0.1K was obtained from the resistivity versus temperature measurements for different applied ac currents. The temperature dependence of the critical current was fitted with a power law: J c(T)= J c(0)[1− T/T c] n with n =2. The critical current in self-field at 77K was found to be 8×103 A/cm2. The temperature dependence of the real and imaginary parts of ac susceptibility was measured for different amplitudes of ac magnetic field. Only a small differences of the ac susceptibility for parallel and perpendicular fields with respect to the film surface were observed. [Copyright &y& Elsevier]

Abstract: The critical currents and the resistances in the top and the bottom surface layers have been studied in 2H-NbSe2single crystal using the flux transformer geometry. In the peak effect region, the critical currents and the resistances in the top and bottom surface layers have distinctly different values. These results are tentatively understood in terms of an order–disorder transition and have implications for the correlations of the vortex lattice throughout the sample. [Copyright &y& Elsevier]

Measurements of non-local in-plane resistance originating from transverse vortex–vortex correlations have been performed on Bi2Sr2CaCu2O8+δ single crystals in a magnetic field up to 9 T applied along the crystal c-axis. Our results demonstrate that a rigid vortex lattice does exist over a broad portion of the magnetic field–temperature (H–T) phase diagram, well above the first-order transition boundary HFOT(T). [Copyright &y& Elsevier]

Abstract: Localization of vortex lines on columnar defects introduced in BSCCO:2212 crystals by heavy ion irradiation is supposed to enhance the critical current J c to the depairing limit . In experiments, the increase of the magnetic irreversibility is not accompanied by suppression of flux creep, even at low temperatures. This impedes the determination of J c . Using the Hall-array technique, we have determined the dependence of the energy barrier for flux creep U on current density J at various temperatures and applied magnetic fields. On the basis of the functional form of U(J) dependence, we identify three regimes of flux creep: from linear, Kim-Anderson like, at high currents, to logarithmic at intermediate currents, and power law at low currents. Critical currents determined from U(J) variations, lie orders of magnitude below the depairing current, indicating that the mechanism of creep is different from the half-loop nucleation predicted in the Bose-glass model. [ABSTRACT FROM AUTHOR]

Abstract: The effect of substitution of rare-earth (RE), Tb on the critical current density (J C), pinning potential (U 0) and flux pinning properties of (Bi,Pb)-2212 superconductor was studied. The XRD and EDS analyses show that Tb-atoms are successfully substituted into the (Bi,Pb)-2212 system. The critical temperature (T C), self-and in-field J C of Tb-substituted samples are found to be highly enhanced for optimum doping levels. The sample with x =0.075 shows the maximum flux pinning force (F P ) of 275×104 Nm−3 and the peak position of F P shifts to higher fields (0.84T) as against 3.0×104 Nm−3 and 0.12T for the pure-sample. In addition, the values of self-field J C and U 0, calculated using Anderson''s function are maximum for this sample (x =0.075). The Dew-Hughes pinning analysis shows that the main pinning mechanism is due to the point-defects brought about by the substitution of Tb-atoms at the Sr-site. The enhancements in J C(B) characteristics, values of U 0, irreversibility field (B irr) and F P are of great scientific and technological significance and are explained on the basis of hole optimization and formation of point-defects due to the substitution of Tb at Sr-site of (Bi,Pb)-2212 system. [Copyright &y& Elsevier]