| Since superconductivity in Hg was firstly discovered by Heike Kamerlingh Onnes before one century, scientists have been searching for new superconductors with higher transition temperature (Tc) and trying to explore the micro-mechanism of superconductivity. In 1986, superconductivity with Tc=35 K in copper-oxide ceramics was discovered by Bednorz and Muller, and the highest Tc～164K at a high pressure in the Cu-oxides has been obtained. In the early of 2008, superconductivity with 26K in LaO1-xFxFeAs was discovered by Hosono et al, a Japanese scientist. More superconductors were obtained by replacing La by other lanthanides, partly substituting F for O (electron doped), or Sr for La (hole doped), or applying high pressure in the synthesis or measurement process. In these superconductors, the highest Tc reached to 56K, which terminates the monopoly position of the copper oxides in the high temperature superconductors (HTSC) and heralds a new era in superconducting research. After hard work in the past three years,5 kinds of Fe-based superconductors, ReO1-xFxFeAs(Re=rare earth), (Ba, K)Fe2As2, LiFeAs, Fe(Se,Te) and (Tl, K, Rb, Cs)FexSe2 have been discovered, they contain a similar Fe-layer. Except for cuprates, iron-based superconductor is another unconventional type of HTSC containing a transition metal. Studies on their crystal structure, electronic structure, magnetic property and superconductivity were carried out in the past years. Understanding on these systems has been deepened more and more.Base on the previous research on the Fe-based superconductors in our group, we choose the Fe(Te,Se) system with the simplest structure to study the substitution effect of Cu for Fe and the influence of excess Fe atoms on superconductivity. We get Fe1-xCuxTe0.5Se0.5(0≤x≤0.3) single crystals. At first, we annealed the samples in air, and found that the excess Fe atoms can be partially removed and superconductivity can be improved. A systematic research on their structure, transport and magnetic properties was carried out. The paper is divided into four chapters. First chapter presents a review on the research history of superconductivity. We are focusing mainly on the research progress on Fe-based superconductors, and introduce the motivation of this work. Second chapter introduces the experiment methods used in this paper. The experiment results of Fe1-05-xCuuSe0.5Te0.5 system were reported in Chapter 3. Chapter 4 gives a summary for this paper. The main conclusions are as follows:We have successfully grown the Cu-doped Fe1.05-xCuxSe0.5Teo.s single crystals using self-flux method. With increasing Cu content, x value, the lattice parameters a, and c increases and decreases monotonically, respectively. For x≥0.3, an impurity of CuFeSe2 was found in the crystals. For 0≤x≤0.05, the Tc value decreases with x increase. For x≥0.06, the superconductivity disappears and the conductivity follows a two-dimensional variable-range hopping mechanism. The magnetization measurements indicate that a long rang magnetic order does not occur in the crystals. It was suggested that the partial substitution of Cu for Fe results in a localization of carriers, suppresses superconductivity in this system. These results have an important role for the understanding on the mechanism of superconductivity in Fe-based superconductors.
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