Pinning in a porous high-temperature superconductor Bi2223

Abstract

The current-voltage characteristics of a porous superconductor Bi 2 Sr 2 Ca 2 Cu 3 O x (Bi2223) have been measured at temperature range from 10 to 90 K. The experimental dependences have been analyzed within the model allowing for pinning by clusters of a normal phase with fractal boundaries, as well as the model taking into account phase transformations of vortex matter. It has been found that the electrical resistance of the superconductor material significantly increases at temperatures of 60-70 K over the entire range of magnetic fields under consideration without changing in the sign of the curvature of the dependence R(I). The melting of the vortex structure occurs at these temperatures. It has been assumed that this behavior is associated with the specific feature of the pinning in a highly porous hightemperature superconductor, which lies in the fractal distribution of pinning centers in a wide range of self-similarity scales.

Highly Porous Superconductors: Synthesis, Research, and Prospects

“…For Bi2223 porous polycrystals, the fractal dimension of the boundaries of pores and granules was determined from micrographs by covering with squares [27,102]. The fractal dimension of boundaries on a plane can range from 1 (smooth boundaries and narrow pore size distribution) to 2 (maximum tortuosity and wide pore size distribution).…”

“…The current-voltage characteristics of Bi2223 porous polycrystals [27,102,127,128] and Bi2212 fabrics [115] have a nonlinear form, typical of bulk HTSCs [129]. With increasing current, the voltage drop across the samples gradually increases.…”

“…At H > H cJ , in polycrystalline superconductors, nonzero resistance appears. Since the area of contact points of neighboring granules is one to two orders of magnitude smaller than that in dense polycrystalline HTSCs, the resistance of Bi2223 porous polycrystals is more sensitive to changes in the external magnetic field [102,118,130]. The magnetoresistance of the Bi2223 porous polycrystal exhibits an inverse hysteresis [130]: the resistance with an increase in the external field is greater than that with a decrease.…”

SUPERCONDUCTING PROPERTIES OF Y2Ba5Cu8Oδ (Y258) POROUS AND NON- POROUS STRUCTURE

“…Materials in foam and porous structures can be considered as a novel class among bulks, films and single crystal since this materials have specific properties that has potentially high critical temperature as well as critical current density (J c ) [1]. A porous high temperature superconductor material can be considered as an aggregate of single crystals that are spatially separated and attach each other predominantly through their faces [2]. Materials containing tailored porosity exhibit special properties and features that usually cannot be achieved by their conventional dense counterparts [3].…”

Effect of Eu Substitution in Low Density Bi (Pb)-2223 High Temperature Superconductors

“…In spite of that, it is interesting to evolve the properties of these doped materials in low-density form with pores. A porous temperature superconductor material is an aggregate of single crystals that are spatially separated and touch each other predominantly through their faces [6,7]. Ceramics with porous and foam structures have the ability in tailoring various physical properties [8] which provide many solutions for some problems encountered in the applications of bulk or film type superconductors such as reducing hot spot formation and decreasing thermal inertia [9,10].…”