Solvothermal Synthesis Of Metastable Structures Of Ⅰ-Ⅲ-Ⅵ₂ Ternary Sulphides And Its Characterizations

This dissertation reported the preparation of newly metastable structure ofâ… -â…¢-â…¥₂ ternary sulphides.Wurtzite CulnS₂ and wurtzite CuGaS₂ 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 ofâ… -â…¢-â…¥₂ ternary semiconductors.In addition,chalcopyrite CuInS₂ 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 CuInS₂ nanostructures have been successfully prepared though simple solvothermal procedures.By using CuSO₄·5H₂O,InCl₃·4H₂O and thiourea as the starting materials,and N,N-dimethylformamide(DMF) as solvent, chalcopyrite CuInS₂ 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 CuInS₂ hollow spheres.In the similar experiment conditions,three-dimensional CuInS₂ flowerlike architectures with a diameter about 3.5μm have been fabricated when Cu(NO₃)₂·5H₂O was used as Cu²⁺ sources.These flowerlike architectures are made up of dozens of flakelike nanopetals with a thickness about 30nm.The reaction times,temperature and Cu²⁺ sources play key roles in the formation of the flowerlike architectures.The optical and electronical properties of the obtained CuInS₂ nanostructures were investigated.2.A new phase of nanostructured CuInS₂,which was indexed as wurtzite structure,a metastable,cation disordered polymorph of CuInS₂,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 CuInS₂ were investigated.In detail,it plays three important roles:(1) solvent,(2) reducing agent, Cu²⁺ was reduced to Cu⁺,and(3) ligand.The thermal stability of wurtzite CuInS₂ was investigated and the result shows that that wurtzite CuInS₂ is a metastable,high energetic structure.The relationship between crystal structure and physical properties were discussed.We studied the optical properties of wurtzite CuInS₂.And the visible and near-infrared absorption spectra show that the as-prepared wurtzite CuInS₂ has distinct optical absorption properties and band gaps compared with chalcopyrite CuInS₂.3.By controlling the reaction parameters and optimizing the reaction conditions, a newly metastable wurtzite structure CuGaS₂ 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 CuGaS₂.The reaction temperature plays an important role in the formation of wurtzite CuGaS₂.Cu_7.2S₄ always coexisted when the temperature was too low,while chalcopyrite CuGaS₂ always coexisted when the temperature was too high.The photoluminescence property of wurtzite CuGaS₂ is investigated,which clearly shows that the PL property of wurtzite CuGaS₂ is quiet different from that of chalcopyrite CuGaS₂.