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

• Published in: Physica. C, Superconductivity Superconductivity, 2003-02, Vol.384 (4), p.491-500
• Main Authors: Muné, P., Govea-Alcaide, E., Jardim, R.F.
• Format: Article
• Language: English
• ISSN: 0921-4534
• DOI: 10.1016/S0921-4534(02)02060-9

The hysteretic behavior of the superconducting 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 XRD 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 SEM which revealed grains with platelet-like geometry and typical dimensions of 3x1 mm2 and thickness of 0.5 mm. Results of magnetization versus applied magnetic field performed in powder samples indicate that the lower critical field Hcl > 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 Jc > 6.6x108 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. Authors have found that the grain properties are 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. 22 refs.