Preparation, Crystal Structure And Electromagnetic Properties Of Nb-based Chalcogenides

In this thesis, we focus on the Nb-based chalcogenides superconductivity, which includes NbSe2 single crystal, Zr doped NbSe2 compounds, Cu(or Li) doped NbS2 compounds. The chief research contents about these compounds consists of the preparation method, crystal structure and electromagnetic properties.The main results are listed as follows.1) Dual-temperature tube furnace is generally used to grow single crystal by chemical vapor transport(CVT). We have successfully employed the temperature gradient of single-temperature tube furnace to grow NbSe2 single crystal by CVT. The result of measurement show that the NbSe2 crystals have a typical dimensions of 2×2mm2. The single crystal NbSe2 shows superconducting transition at 7.1K with a transition width about 0.3K. The estimated superconducting volume fraction is around 79%. The method employed in this study can be also applied to grow other single crystals by CVT.2) When we explore the influence of hole doping on NbSe2 superconductivity, the doping samples ZrxNb1-xSe2(0≤x≤0.08) are firstly prepared. Their crystal structure and superconducting properties varying with doping amount are investigated. The result show that with the Zr content increasing, the lattice parameters of samples increase slightly and the Tc value decreases in derivative compounds. When x<0.02, superconducting transition temperatures of the samples decrease quite slowly, when x>0.02, a rapid decline of Tc can be clearly observed where the lattice parameters have a sharp increase. The change of superconducting transition temperature is possibly caused by the increase of lattice parameters and a decrease in N(EF), which results from hole doping.3) The low temperature electromagnetic properties and detailed crystal structure parameters of Cu3Nb17S37 and CuxNbS2(x=0.125,0.25) samples have been firstly researched. The result show that the doping samples form a 2a0×2a0 hexagonal superstructure. With the Cu content increasing, the lattice parameters c is constantly increasing, electrical resistivity and magnetic susceptibility are gradually decreasing. All samples show a metallic and paramagnetic behavior.4) The LixNbS2(0≤x≤0.5) samples have been successfully prepared by solid state reaction and their crystal structure and electromagnetic properties varying with doping amount are investigated. The result show that with the Li content increasing, the phase of this system changes from 3R phase to 2H phase, the lattice parameters c has an increase, electrical resistivity and magnetic susceptibility show a tendency of decrease and increase respectively. All samples show a metallic and paramagnetic behavior.