Both the critical current intensity at zero applied magnetic field Ic(T), from nitrogen temperature up to the critical temperature, and the normal‐state resistivity ρn(T) have been measured in granular Bi1.5Pb0.5Sr2Ca2Cu3Oy (BiPbSCCO) superconductors, with different granular characteristics. It is found that the combination [Ic(T)/P][ρn(0)/ρ’n], where ρ(0) is the residual normal‐state resistivity, ρ’n is the temperature derivative and P is the sample’s perimeter, is essentially constant from sample to sample at any temperature. It thus constitutes a universal temperature‐dependent critical current for the polycrystalline BiPbSCCO family.

Critical currents versus normal‐state resistivity in granular BiPb‐based copper‐oxide superconductors

Measurements of the AC susceptibility of HTSC ceramic samples were performed not only for different values of the AC magnetic field, but also for different sample sizes, thus obtaining information of the temperature interdependence of penetration field and penetration depth for the intergranular phase transition. To fit the experimental data, the critical state model was modified by introducing a power law to the magnetic field dependence of the critical current. While the YBCO sample showed a dependency of the critical current density on the magnetic field with an exponent of approximately 3.5, the field dependency exponent for the BSCCO sample turned out to be only 0.7. The temperature dependence of the intergranular critical current densities shows large exponents supporting flux creep dominated behaviour for the samples investigated.

Size dependence of the AC susceptibility and critical current densities of ceramic high-Tc superconductors

The H-T diagram describing the critical current behaviour of granular superconductors in a magnetic field is proposed. The process of trapping magnetic field by a ceramic sample and the influence of the trapped field on the transport critical current have been studied. The temperature and magnetic field dependences of intergrain and intragrain critical currents have been analysed.

https://iopscience.iop.org/article/10.1088/0953-2048/5/6/002/pdf

Critical currents of granular YBa2Cu3O7- delta superconductors

The effects of annealing under reducing atmosphere on BSCCO 2212 textured thick films prepared by partial melting techniques are reported. The influence of the atmosphere on the 2212 crystalline structure and chemical composition, as well as on the superconducting properties ( T c,0 and J c ), is discussed. The value of T c,0 can be varied by annealing at different temperatures and for different times, reaching a maximum (85 K) for the films annealed at 500°C for 4 h. Transport J c was found to be dependent on the annealing conditions (the maximum was 1.6 × 10 3 A / cm 2 at 77 K and zero applied magnetic field for the films annealed at 500°C for 2h), decreasing for long annealing treatments at fixed temperatures. The magnetization measurements showed a strong field and temperature dependence of J c .

Effects of annealing under reducing atmosphere on BSCCO 2212 textured thick films prepared by partial melting techniques

The penetration of a magnetic field into superconducting grains and weak links of YBa2Cu3O7−δ ceramic high-temperature superconductors is investigated using measurements of the transverse and longitudinal magnetoresistances at T=77.3 K and 0≤H≤∼500 Oe as a function of the transport current in the range ∼0.01≤I/I

 c
 ≤∼0.99. The effects associated with the complete penetration of Josephson vortices into weak links of the high-temperature superconductor in magnetic fields H

c2J
, the onset of penetration of Abrikosov vortices into superconducting grains in magnetic fields H

c1A
, and the first-order transition from the Bragg glass phase to the vortex glass phase in fields H
BG-VG are revealed and interpreted. The I-H phase diagrams YBa2Cu3O7−δ high-temperature superconductors are constructed for I ⊥ H and I ‖ H.

Penetration of a magnetic field into the YBa 2 Cu 3 O 7−δ high-temperature superconductor: Magnetoresistance in weak magnetic fields

Three magnetic field ranges corresponding to different critical current density Jc behavior have been discovered. They correlate with grain magnetization changes. The first field range corresponds to the grain Meissner phase, the second one to the partial penetration of magnetic fluxoids into a grain, and the third one to the complete vortex penetration. For the first interval, the dependence Jc(H)=Jc(0)/[1+(H/H0)2] is valid. The inverse critical current density is shown to depend linearly on the sample cross-section due to the magnetic field self-induced by the flowing current.

The effect of magnetic field on the critical current of YBa2Cu3Ox ceramics

Three magnetic field ranges corresponding to different critical current density j c behavior have been found out. They correlate with grain magnetization changes. The inverse critical current density is shown to depend linearly on the sample cross-section due to the “own” magnetic field induced by the flowing current.

Magnetic field dependence of the critical current density in YBa2Cu3Ox ceramics

The intergrain and intragrain parameters of critical current in YBa 2 Cu 3 O 7-δ ceramics were studied. The “H-T” diagram describing the behavior of ceramic HTSC samples in magnetic field is proposed.

Magnetic field and temperature dependence of critical current and magnetization in YBa2Cu3O7-δ ceramics

Magnetic field dependence of ceramics critical current and magnetization in YBa2Cu3O7-δ

The Ag YBa2Cu3O7−y composites with the different Ag-volume fraction x were studied The critical current density jc of the Ag2O-based material decreases with x For Ag-based material the maximum of the jc(x)_dependence at x∼20% seems to be caused by a larger sample density Measurements of the current-voltage characteristics and the effect of magnetic field on the critical current show that the silver addition changes the type of the intergrain links

D.A. Komarkov

Papers

The effect of magnetic field on the critical current of YBa2Cu3Ox ceramics

Magnetic field dependence of the critical current density in YBa2Cu3Ox ceramics

Magnetic field and temperature dependence of critical current and magnetization in YBa2Cu3O7-δ ceramics

Magnetic field dependence of ceramics critical current and magnetization in YBa2Cu3O7-δ

Superconductivity in AgYBa2Cu3O7−y composites