Substitution of Sm at Ca site in Bi1.6Pb0.4Sr2Ca2-xSmxCu3Oy superconductors
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We have investigated the effect of the partial substitution of Ca by Sm in the Bi-2223 superconducting samples prepared by standard solid-state reaction method. Our investigations consisted of DC electrical resistivity, AC susceptibility, X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements. We measured the critical transition temperatures, activation energies and irreversibility lines from the resistivity versus temperature curves under DC magnetic fields in the range of 0 and 0.6T. The superconducting transition temperature, T-c, and activation energy, U-0, were found to decrease with increasing Sm concentration and with increasing applied magnetic field. Increasing the Sin content shifted the irreversibility temperature to lower values. The AC susceptibility measurements were carried out at 80 A/m field strength and f = 211 Hz frequency. XRD patterns and SEM micrographs are given to provide information about Bi-2223 and Bi-2212 phases and their grain size. The possible reasons for the observed degradation in microstructural and superconducting properties due to Sm substitution were discussed. (c) 2007 Elsevier B.V. All rights reserved.