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In this paper, we investigated the influences of Na substitution on the enhancements of critical current density (J c) in the BiPbSrCaCuO (BPSCCO) superconductors. The Bi 1.6 Pb 0.4 Sr 2 Ca 2¹x Na x Cu 3 O 10+¤ (where x was ranged from 0 to 0.1) polycrystalline samples were fabricated using solid state reaction technique. The zero electrical critical temperature (T c) of Na-substituted BPSCCO samples was found to be slightly higher than that of Na-free BPSCCO one. Magnetization J c data measured at 65 K with field applied parallel to the c-axis of the samples showed that J c of Na-substituted BPSCCO samples were enhanced. Possible reasons for the J c enhancements were attributed to the effective flux pinning by crystal defects at Ca layers generated by Na substitution. Improvements of volume pinning force (F p) in terms of magnitude and position of F pmax were also obtained.

This study discusses the crystal structure and magnetic properties of the rare-earth doped La 0.8 R 0.2 (Fe 0.88 Si 0.12) 13 (with R = Sm, Tb) compounds. All the samples were prepared by using arc-melting technique in argon atmosphere and the obtained result shows that after heat treatment, the samples exhibited the NaZn 13-type cubic phase with a small amount of a secondary ¡-Fe phase. The magnetic properties and magnetic entropy change were determined by mean of the temperature and field dependence magnetizations. Besides the decrease in the lattice constants, there was also observed a significant increase of Curie temperature and magnetic entropy change ¹¦S M which reached a maximum of 4.5 J/kg K for La 0.8 Sm 0.2 (Fe 0.88 Si 0.12) 13 , corresponding to a relative cooling powers (RCP) of 102 J/kg for the sample.

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