Synthesis By Chemical Vapor Transport Process,Morphology And Properties Of The Bimetallic Sulfides

Bimetallic sulfides with rich chemical composition and the unique optical,electrical, magnetic and other properties have caused the huge interest of scientists,eventually became an integral part of the study on the sulfur-containing compounds inthe study. In recent years, experimental design, morphology, structure and chemicalproperties of bimetallic sulfides are one of the very active research areas. It has gonethrough years of change, and now entered a new era, namely, from the simplesynthesis to the new phase of structure control and directional assembly. In addition,the research of morphology, especially on nano-size, has been a popular topic inmaterials science, since the morphology, size, surface condition and other changeswill affect the physical and chemical properties of the materials. In summary, closelyaround the features, experimental design of the new bimetallic sulfide and assemblyof controlled morphology, now are main task about bimetallic sulfide. This workselects two representative and important bimetallic sulfides system of misfit-layeredsulfides and intercalation compound Fe_1/3TaS₂to study.1. PbTS₃（T=Ti, Nb, Ta） are the typical misfit-layered compounds （MLCs）, dueto their application as superconduct and lubricate materials.Here we report the synthesis of high-purity PbTiS₃single crystals through achemical vapor transport （CVT） process with the sponge titanium as titanium source.And the best heating temperature is650℃, reaction time is6days.2. For the first time, we report the preparation and characterization of curl-likePbNbS₃and PbTa2S5through a CVT process at850℃and750℃respectively for6days with each metal and sulfur as reactants. The morphology of curl-like PbNbS₃and PbTa2S5was first discussed during chemical reaction. The parameters of the reaction, such as temperature, time and ratio of reactants, were studied to understandthe effects of crystal growth. The XRD, XPS, Raman and other tests were undertakenfor the flake and tubular PbNbS₃, indicating that the two kinds morphology ofPbNbS₃are different in the electronic structure, crystal structure and so on.3. Combining with the experiments of Pb-Ti-S system, the observations of thegrowth nuclei suggests a formation and growth mechanism based on the spontaneouscurling up of thin triangular flakes as a consequence of the lattice parameterdifference between the constituent subsystems.4. The sulfide nanostructures can be fabricated directly on metal substrates via asimple gas-solid route. The defining characteristic of this growth strategy is that metalacts both as the substrate and the metal source for growing of the nanostructures. Thesulfide nanostructures are grown in-situ and adhered on the metal substrate withoutusing templates or catalysts. The assembly of nanostructures on the underlyingsubstrate has the virtues of simplicity, efficiency, and low cost. In this thesis, Ta foilswere used as the Ta source as well as substrate for the growth of Fe_1/3TaS₂hexagonalnanoplates.To preparation of Fe_1/3TaS₂hexagonal nanoplates, the tubes with reactants areevacuated and sealed, then heated at700℃for8h. The products are hexagonalnanoplates with a border length of～350nm and thickness range⁴0nm.In summary, we have demonstrated two effective approachs of chemical vaportransport （CVT） method and metal substrate CVT method, for the preparation ofhigh-purity PbTiS₃single crystals, curl-like PbNbS₃and PbTa2S5, Fe_1/3TaS₂hexagonal nanoplates. We also studied the structure, morphology and opticalproperties of products. In conclusion, our works provide examples and information tothe research of bimetallic sulfides, and develop the application of the CVT methods inmaterials synthesis.