Gd katkılanmış Bi-2223 süperiletkenlerin fiziksel özelliklerinin incelenmesi

Many researchers have studied the effect of addition or substitution of different elements to high temperature superconductors. The aim in these studies is twofold; to understand the underlying mechanism of high temperature superconductivity and to enhance the mechanical and superconducting properties of the high temperature superconductors. The second purpose is especially important for the technological applications of the high temperature superconductors. Copper oxides (cuprates) are the most important group of high temperature superconductors. Among cuprates, the BSCCO system is widely studied and some technological applications are achieved. In this thesis, the effect of addition of Gd on the superconducting and mechanical properties of Bi-2223 phase is analyzed. The Gd ions are believed to substitute the Ca ions of the BSCCO system. This is evidenced by the decrease of transition temperature (Tc) which is related to the charge carrier concentration and the decrease in the c parameter of the unit cell. The ionic radius of Gd is smaller than that of Ca so the decrease in the c parameter can be explained in terms of the difference in the radii. From the decrease of critical current density (Jc) values and SEM observations it is believed that the grain connectivity of the samples with increasing Gd content degraded. Weak link behaviour increased with the addition of Gd. The addition of Gd degraded the formation of the 2223 phase and hence as the Gd content increased, the volume fraction of 2223 phase decreased while that of 2212 increased. The high magnetic moment of Gd possibly affected the Cooper pairs in the superconducting phase. The spins of the pair may have been adversely affected by the magnetic moment of Gd which also resulted in the decrease of carrier concentration by pair-breaking mechanism. The results of this thesis showed that Gd addition degraded the superconducting and mechanical properties of the BSCCO system.