E. Govea-Alcaide

Influence of the compacting pressure on the dependence of the critical current with magnetic field in polycrystalline (Bi-Pb)2Sr2Ca2Cu3Ox superconductors

The hysteretic behavior of the superconducting critical current density Jc(Ba) dependence under low applied magnetic fields (Ba<50 mT) of nearly single phase Bi1.64Pb0.36Sr2Ca2Cu3O10 Bi-2223 samples was investigated. The samples were prepared from the same batch obtained by solid-state reaction method, pressed uniaxially at compacting pressures ranging from 40 to 250 MPa before the last heat treatment. The presence of up to ∼10% of additional phases such as Bi-2212 and Ca2PbO4 was estimated from the analysis of the X-ray diffraction patterns. These results also indicate that higher compacting pressures yielded a reduced volume fraction associated with the extra phases. The granular structure of these samples was studied by scanning electron microscopy which revealed grains with platelet-like geometry and typical dimensions of ∼3×1 μm2 and thickness of ∼0.5 μm. Results of magnetization versus applied magnetic field performed in powder samples indicate that the lower critical field Hclg∼10 mT at 77 K is sample independent. In addition, the estimated intragranular current density Jcg at 77 K by using the Bean model yields Jcg≈6.6×108 A/m2, which is in excellent agreement with the literature. Measurements of electrical resistivity and magnetization as a function of temperature were performed and compared to Jc(Ba) measurements. We have found that the grain properties are very similar in all samples but that the Jc(Ba) dependence is very sensitive to the compacting pressure. The experimental data are discussed within the framework of a three-level superconducting system.

Magnetic hysteresis of the critical current density of polycrystalline (Bi–Pb)–Sr–Ca–Cu–O superconductors: a fingerprint of the intragranular and intergranular flux trapping

Abstract The hysteretic behavior of the superconducting critical current density Jc(Ba) dependence under low applied magnetic fields (B a mT ) of polycrystalline Bi1.64Pb0.36Sr2Ca2Cu3Oy samples was investigated. All the samples were prepared from the same powder but subjected to different pressures ranging from 40 to 250 MPa before the last heat treatment. The samples were characterized by scanning electron microscopy and X-ray powder diffraction analysis. The magnetic behavior of the superconducting grains was studied by measuring magnetization versus applied magnetic field in powder samples. The Jc(Ba) data are discussed within the scenario of the three-level superconducting system.