Solvothermal Synthesis of Metastable Structures of Ⅰ-Ⅲ-Ⅵ_2 Ternary Sulphides and Its Characterizations
This dissertation reported the preparation of newly metastable structure ofⅠ-Ⅲ-Ⅵ_2 ternary sulphides.Wurtzite CulnS_2 and wurtzite CuGaS_2 have been successfully prepared under milder conditions.These newly metastable structures are stable at room temperature.The formation mechanism of wurtzite structure was systemically investigated.The optical properties of wurtzite structure were studied and compared with the corresponding stable phase,in order to the find out relationship between crystal structure and physical properties.It is expect that these new phases will bring novel properties and expand applications ofⅠ-Ⅲ-Ⅵ_2 ternary semiconductors.In addition,chalcopyrite CuInS_2 nanostructures have been successfully prepared via a simple solution-based route.The detailed contents can be summarized as follows:1.A few of novel chalcopyrite CuInS_2 nanostructures have been successfully prepared though simple solvothermal procedures.By using CuSO_4·5H_2O,InCl_3·4H_2O and thiourea as the starting materials,and N,N-dimethylformamide(DMF) as solvent, chalcopyrite CuInS_2 hollow spheres have been prepared.Based on the observations of intermediate products at different reaction stages,a mechanism of Ostwald ripening is proposed for the formation of CuInS_2 hollow spheres.In the similar experiment conditions,three-dimensional CuInS_2 flowerlike architectures with a diameter about 3.5μm have been fabricated when Cu(NO_3)_2·5H_2O was used as Cu~(2+) sources.These flowerlike architectures are made up of dozens of flakelike nanopetals with a thickness about 30nm.The reaction times,temperature and Cu~(2+) sources play key roles in the formation of the flowerlike architectures.The optical and electronical properties of the obtained CuInS_2 nanostructures were investigated.2.A new phase of nanostructured CuInS_2,which was indexed as wurtzite structure,a metastable,cation disordered polymorph of CuInS_2,has been synthesized by a solvothermal method.In this structure,Cu and In atoms randomly occupy the cation sublattice positions.Based on the experiment results,it is suggested that a kinetics-controlled process reduced the energy barrier,allowing the formation of a metastable phase.The roles of ethanolamine in the formation of wurtzite CuInS_2 were investigated.In detail,it plays three important roles:(1) solvent,(2) reducing agent, Cu~(2+) was reduced to Cu~+,and(3) ligand.The thermal stability of wurtzite CuInS_2 was investigated and the result shows that that wurtzite CuInS_2 is a metastable,high energetic structure.The relationship between crystal structure and physical properties were discussed.We studied the optical properties of wurtzite CuInS_2.And the visible and near-infrared absorption spectra show that the as-prepared wurtzite CuInS_2 has distinct optical absorption properties and band gaps compared with chalcopyrite CuInS_2.3.By controlling the reaction parameters and optimizing the reaction conditions, a newly metastable wurtzite structure CuGaS_2 was prepared by a solvothermal method. The effects of solvents on the phase of the products were carefully investigated and the result shows that ethylenediamine or the admixture of ethylenediamine and 3-amino-1-propane are suit for the formation of wurtzite CuGaS_2.The reaction temperature plays an important role in the formation of wurtzite CuGaS_2.Cu_(7.2)S_4 always coexisted when the temperature was too low,while chalcopyrite CuGaS_2 always coexisted when the temperature was too high.The photoluminescence property of wurtzite CuGaS_2 is investigated,which clearly shows that the PL property of wurtzite CuGaS_2 is quiet different from that of chalcopyrite CuGaS_2.