Superconducting Properties Of Carbon And Zn Double-doped Mg_1-xZn_x(B_1-xC_x)₂

The history of superconductivity, the basic properties of superconductivity, BCS theory, the kind of superconductor and its current research were simply introduced in the dissertation at first. Then, the dissertation mainly describes the following work.Firstly, we described the effects on Superconducting properties of carbon and Zn double-doped Mg_1-xZn_x(B_1-xC_x)₂. A serious of polycrystalline samples of Mg_1-xZn_x(B_1-xC_x)₂ (x = 0.00, 0.02, 0.04, 0.06, 0.08, and 0.10) were synthesized by conventional solid state reaction method. Phase identification, crystal structure and superconducting transition temperature (Tc) were studied by means of X-ray diffraction (XRD) and resistivity measurements. The results indicated that the lattice parameters a and c show no clear trend in its changes with increasing doping level, it was turned out that the dopants had a marked effect on the crystal lattice parameters and changed the crystal structure of the samples. The Tc for Mg_1-xZn_x(B_1-xC_x)₂ decreased with C and Zn doping, but the rate of decrease was slower than single C-doped.Secondly, we described the effects on Superconducting properties of Cu-doping (Mg1.1B2)1-xCux. MgB₂ samples with 3 at. % Cu addition were synthesized by conventional solid state reaction method at 850℃under a background pressure about 10-3 Pa. Phase identification, crystal structure and superconducting transition temperature (Tc) were studied by means of X-ray diffraction (XRD) and resistivity measurements. The results indicated that the 3 at. % Cu addition mainly reacted with the Mg forming the Mg–Cu alloys and, thus, there was little Cu substitution in Mg occurring in the MgB₂ crystal structure. The resistivity measurements indicated that the Tc is nearly unchanged by the 3 at. % Cu doping, it is around 38.25 K.