Analysis of thermo-magnetic fluctuations above the glass-transition temperature in Bi1.6Pb0.5Sr2−xEuxCa1.1Cu2.1O8+δ (0.000 ≤ x ≤ 0.180) system

The resistivity of Bi_1.6Pb_0.5Sr_2−xEu_xCa_1.1Cu_2.1O_8+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 [U₀(B)] and the temperature and magnetic field dependent activation energy [U₀(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 0.8 T) is obtained and this scaling is quite useful for better understanding of the behavior of the flux vortices in high temperature superconductors.     

Influence of sintering temperature on microstructure,critical current density and pinning potential of superconducting Bi1.6Pb0.5Sr1.8Dy0.2Ca1.1Cu2.1O8+δ ceramics

The influence of sintering temperature on the microstructure, critical current density (J_C), pinning potential values (U₀) and flux pinning properties of Bi_1.6Pb_0.5Sr_1.8Dy_0.2Ca_1.1Cu_2.1O_8+δ superconductor has been investigated. The samples are prepared by the solid-state route and sintered at temperatures ranging from 846 to 860 °C. A systematic correlation between the sintering temperature, Lotgering index, J_C, U₀ and flux pinning properties has been found. The samples sintered at lower sintering temperature (846 °C) have more grain boundaries with smaller grains while those sintered at a higher temperature (856 °C) contain larger grains with good texturing. The flux pinning force (F_P) calculated from the field dependent J_C values shows that the irreversibility lines (IL) of the Dy-doped samples shift towards higher fields to different extents depending on the sintering temperature. The maximum value of F_P = 1697 kN m^?3 is obtained for the sample sintered at 846 °C and the peak position of F_P is obtained at 0.96 T as against 616 kN m^?3 and 0.52 T for the sample sintered at 856 °C. The U₀ values calculated by Anderson's function is maximum for the sample sintered at 846 °C. But the self-field J_C value of this sample is lower than that of the samples sintered at 856 °C. The samples sintered at 856 °C show best self-field J_C due to the improved microstructure. The changes in microstructure followed by very high enhancement of self-field J_C, J_C(B) characteristics, F_P and U₀ values within a narrow temperature range, are of great scientific and technological significance and the results are explained on the basis of microstructural variation with respect to sintering temperature, hole optimization and formation of point defects due to the doping of Dy atoms in Bi_1.6Pb_0.5Sr_1.8Dy_0.2Ca_1.1Cu_2.1O_8+δ system.     

Doping dependent metal to insulator transition in the (Bi,Pb)-2212 system: The evolution of structural and electronic properties with europium substitution

The present work investigates the effect of europium substitution on the(Bi,Pb)-2212 system in the concentration range 0.5 ≤ x ≤ 1.0.Phase analysis and lattice parameter calculations on the powder diffraction data and the elemental analysis of EDX show that the Eu atoms are successfully substituted into the(Bi,Pb)-2212 system.Resistivity measurements(64-300 K) reveal that the system exhibits superconductivity at x ≤ 0.5 and semiconductivity at x > 0.5.With the complete suppression of superconductivity which is known to be a quasi-two dimensional phenomenon in these materials,a metal to insulator transition takes place at x = 0.6 and the predominant conduction mechanism is found to be variable range hopping between localized states,resulting in macroscopic semiconducting behaviour.The results of electrical and structural properties of the doped(Bi,Pb)-2212 compounds suggest that the decrease of charge carrier concentration and the induced structural disorder are the more effective and dominant mechanisms in the origin of the metal to insulator transition and suppression of superconductivity due to Eu substitution at its Sr site.