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In this work, superconducting samples of type (Bi_1.8Pb_0.4)Sr_1.9Ca_2.1Cu₃O_10+δ were prepared, with Pb_0.4 composed of Pb_0.2²⁺ and Pb_0.2⁴⁺ , at different sintering temperatures ranging from 835℃to 855℃. The prepared samples were characterized using x-ray powder diffraction (XRD), scanning electron microscope (SEM), electron dispersive spectroscopy (EDS) and differential scanning calorimetery (DSC). The superconducting properties were investigated using electrical resistivity and transport critical current density. Our results showed that the sample prepared at sintering temperature 845?C has the optimum value of superconducting transition temperature T_c and transport critical current density J_c

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Superconducting samples of TlBa 2 CaCu 2−x Sc x O 7−δ with x = 0.0, 0.025, 0.05, 0.1, 0.15 and 0.2 have been prepared via the solid-state reaction technique. The effect of weak magnetic fields up to 4.4 kG on the electrical resistivity of the prepared samples has been studied to investigate the flux motion for this phase. The results reveal a slight shift in the superconducting transition temperature T c and an increase in the superconducting transition width T with increasing magnetic field. The magnetic field has a small effect on the electrical resistivity in the normal state and in the first stage of transition, whereas the change in the second stage of superconducting transition is very large. The experimental data, in the second stage of superconducting transition, fit well with the thermally activated flux creep model and the activation energy U (B) shows a power law dependence on magnetic field as B −β . Also, the transition width is related to the magnetic field according to the relation T α B n . The values of β and n are strongly dependent on the scandium content. The magnetic field and temperature dependence of the activation energy U (B, T ) is found to be U (B, T ) ∼ T B −η , where η = β + n. The critical current density J c (0) and the upper critical field B c2 (0) are calculated, from the above measurements, as a function of scandium content. Finally, the electronic thermal conductivity κ e , estimated from the Wiedermann-Franz law, is reported at different applied magnetic fields for the prepared samples.

High- superconducting ceramic samples of the form (x = 0.3, 0.5, 0.7, 0.9 and 1) are prepared in a closed quartz tube at C. The electrical resistance versus temperature is measured in the temperature range between 15 K and room temperature. The effect of magnetic field and applied electric current on the second stage of the transition is studied. It is found that the transition does not occur at a definite temperature but in a temperature range which may approach 50 K or even more. This is believed to be due to the very short coherence length ( Å) of HTSCs or to the random motion of the magnetic flux. The results obtained in our work can give some information about superconducting grains and weak superconducting boundaries.