FeSe-11 süperiletken kristal ve tel üretimi ve karakterizasyonu

In this thesis, we have studied Fe(Se,Te) single crystal, polycrystal and wire by using different processes in order to improve the structural and the superconducting properties of Fe(Se,Te) and to dope FeSe with Ag making superconducting crystal and wire from it. Synthesis and characterization of FeSe0.5Te0.5 single crystals prepared by self-flux technique with two different cooling rates of 1.45 and 5.83℃/h have been investigated. The crystal structure of both samples unchanged by using different cooling rate. The superconducting transition temperatures of two samples obtained as magnetization measurement are seen to be 14.62 and 14.38 K for rapid and slow cooling samples, respectively. Fe1+dSe0.4Te0.6 (d = 0, 5, 10 %) polycrystals have been synthesized by using solid state method, in order to investigate the effect of Sulfur annealing in the various amount of excess iron. The as-grown crystals begin to decrease superconducting transition temperature with increasing the amount of iron. After Sulfur annealed, the diamagnetic signal is strongly enhanced and superconducting transition temperature reach up to 14.5 K with incerasing the amount of excess iron. Synthesis and characterization of Ag doped FeSe0.94 polycrystals prepared by melting have been investigated for the as-grown and the annealed samples. The XRD pattern of both samples indicate that it is mainly composed of the tetragonal. Superconductivity appears at temperature ∼ 8 and 9.2 K for the as-grown and the annealed samples, respectively. Fe(Te,Se) wires were fabricated by using in-situ and ex-situ PIT process. For in-situ PIT process, in the Fe(Se,Te) wire, zero resistivity is not observed due to the Fe sheath introduces much excess iron and accompany by evaporation of chalcogenides in the Fe(Se,Te) phase, which degrade the superconductivity. We have successfully obtained zero resistivity for Fe(Te0.3Se0.7)1.5 superconducting wires using ex-situ PIT process for two different heating process, 800°C+5h; 800°C+25min. Apart from that, we have successfully obtained zero resistivity for two different heating process, 400°C+100h+furnace cooling; 400°C+100h+quench, in the Ag-doped FeSe0.94 superconducting wires which were fabricated by using the ex-situ PIT method.