Papers by Author: R. Abd-Shukor

Abstract: This paper reports on the effectiveness of magnetic nanoparticles as pinning center in the Bi-based superconductor tapes. Nanosize γ-Fe2O3 and ultrafine Fe3O4 have been employed to enhance the transport current density of Ag-sheathed-(Bi1.6Pb0.4)Sr2Ca2Cu3O10 superconductor tapes prepared by the powder-in-tube technique. The transport critical current density, Jc of (Bi1.6Pb0.4)Sr2Ca2Cu3O10-(γ-Fe2O3)0.01, sintered at the optimum temperature of 845 oC is 6490 A/cm2 when measured at 77 K. A further single intermediate rolling step increases Jc to 9560 A/cm2. Samples without γ-Fe2O3 prepared under the same condition showed a lower Jc with a maximum of 1560 A/cm2. Similar results are also obtained for ultrafine Fe3O4. Magnetic impurities generally suppress superconductivity. However, our study shows great promise of magnetic nanorod γ-Fe2O3 and ultrafine Fe3O4 as novel pinning centers in enhancing the transport critical density of Ag sheathed Bi-Sr-Ca-Cu-O superconductor tapes. This is in line with previous calculations on frozen flux superconductor with magnetic nanoparticle as pinning centers.

Abstract: Longitudinal and shear ultrasonic attenuation measurements were performed at 10 MHz in HoBa2-xHoxCu3O7-δ (x=0.0 and 0.15) polycrystalline ceramics between 80 K and 285 K. Longitudinal attenuation profiles showed a large peak around 200 K for superconducting HoBa2Cu3O7-δ but not for oxygen-reduced non-superconducting HoBa2Cu3O7-δ. Two longitudinal attenuation peaks at 190 K and 250 K were observed for Ba-substituted HoBa1.85Ho0.15Cu3O7-δ. The high temperature (∼190 K-200 K) peaks are due to absorption of sound energy during interaction of ultrasound wave with mobile oxygen atoms involved in an oxygen rearrangement process involving Cu-O chains of the materials.

Abstract: This paper reports on the effects of Ag addition on physical properties of high temperature superconductors DyBa2Cu3O7-δ (Dy123). A series of the Dy123 - Agx composite was prepared by solid state reaction method with varying amount of metallic silver (x = 0 – 0.3). Resistance versus temperature measurement was done using the four-point-probe method in the temperature range of 79 K to 300 K. Pure DyBa2Cu3O7-δ was found to superconduct with Tc onset of 91 K and Tc zero of 78 K. Addition of Ag at x = 0.05 caused both Tc onset and Tc zero to increase to 93 K and 84 K, respectively. However, Tc onset and Tc zero dropped for higher silver contents. We found that the optimum silver content in DyBa2Cu3O7-δ for best superconducting behavior and hardness is between x = 0.05 and 0.10. Microstructure analysis using SEM and EDAX showed that most of the silver is uniformly distributed along the grain boundaries filling the pores and hence increasing the hardness of the samples.