Preparation, Crystal Structure And Superconductivity Of Transition Metal Sulfide

Mackinawite has the layered structure similar to the famous iron-based superconductor FeSe, and BCS theory calculation indicates mackinawite may be one of the simplest iron-based superconductors. Moreover, mackinawite can be applied in the solar cells and microbial fuel cells, and be used as an absorbent to remove the trace of poisonous metals in water (such as Pb、Hg、Cr and so on). Because the tetragonal FeS belongs to low-temperatured phase structure, it can’t be synthesized at high temperature. The derived product is merely amorphous by the normal solution reaction. To study the physical properties and possible superconductivity of tetragonal FeS, the well-crystallined product is of great importance. In my research papaer the preparation and characterization of mackinawite (tetragonal FeS) were mainly studied and the preparation and superconductivity of S-doped solid solution Fe1+yTe1-xSx (0≤x≤1, y=0,0.12)were explored. The main researching contents and results are as follows:(1) Research on the synthesis methods of mackinawiteWe explore six synthesis methods for synthesizing mackinawite.1. The reaction of ferrous solution and sulfide solution.2. Hydrothermal method.3. Solvothermal method.4. Sol-Gel method.5. Solid state reaction at low temperature.6. The reaction of metallic iron and sulfide solution. The experimental results indicate single-phased mackinawite can been synthesized by the reaction of ferrous solution and sulfide solution. However, the particle size is small, only inone or two nano. No single-phase mackinawite was synthesized by hydrothermal, solvothermal method, the solid state reaction at low temperature and Sol-Gel method. However, by changing the conditions, amorphous FeS with Fe3O4andhexagonal FeS was obtained by sol-gel method. Happily we have successfully synthesized the single-phased mackinawite by the reaction of metallic iron and sulfide solution. What is more. A new synthesis technology was created:the expensive metallic iron wire was substituted by cheap iron powder, the iron powder material was pasted on the magnet to separate from the synthetic mackinawite.(2) Characterization of single-phase mackinawiteThe synthetic mackinawite by the reaction of metallic iron and sodium sulfide solution was characterized by XRD, SEM.The experimental results have shown no impurity peaks were observed in the XRD pattern of crystal mackinawite and all diffraction peaks were the same as that indexed by tetragonal FeS. The refined unit cell parameters by Powder X were separately a=3.676A, c=5.037A, which is close to that reported by the previous article in the well crystallined mackinawite. SEM pattern indicates the sample consists of nanosheets. The lateral size ofnanosheets varies from200nm to500nm, and the average thickness of nanosheets is about20nm. All of these results can proved that the synthetic mackinawite by the reaction of metallic iron powder with sodium sulfide solution is single-phase structure and well-crystallined.(3) Research on the properties of single-phase mackinawiteThe temperature dependence on resistivity and magnetization of mackinawite has been studied.1. The single-phase mackinawite is a good conductor, its resistivity at room temperature is smaller than that of graphite (55-65μΩ·cm), which indicates the big mackinawite may be a metal.2. The temperature dependence on conductivity of single-phase mackinawitewas fitted well with the empirical formula (R2=0.99997). The result explained electrical conduction of the single-phase mackinawite was essentially caused by a thermal activated process.3. The temperature dependence pattern on magnetic susceptibility provides some information that samples showed weaksuperparamagnetic. The result indicated the derived samples were partiallyoxidated by oxygenin air during the preservation and the experimental process, and produced a small amount of magnetic Fe3O4nanoparticles.(4) Study on preparation of Fe1+yTe1-xSx (0≤x≤0.25, y=0,0.12) by the solid-state reaction.XRD pattern results indicate Fe1.12Te1-xSx (0≤x≤0.25) belonged to single-phase material, and the structure of unit cell belonged to tetragonal with space group P4/nmm. The refined cell parameters by Powder X were α=3.8223～3.8160A, c=6.2835～6.2418A. With the increasing of S-doped content, the cell parameters both a and c decrease gradually.(5) Study on temperature dependence on resistivity of Fe1.12Te1-xSx (0≤x≤0.25) by the standard four probes method.The experimental results showed a superconducting transition was observed in the pattern of all Fe1.12Te1-xSx(0.05≤x≤0.3). Moreover, with the increasing of S-doped content. the superconducting transition temperature is gradually reducing. There was zero resistivity to be observed in Fe1.12Te0.8S0.2and Tc is about8K. There were no zero resistivity to be observed in other samples, the reason may be the inhomogeneity of samples.(6) Research on annealing properties of Fe1.12Te0.8S0.2To improve the superconducting transition temperature of Fe1.12Te0.8S0.2, Fe1.12Te0.8S0.2was annealed at473K for5hours. The electrical analysis indicates the superconducting transition temperature was improved from9K to10K after annealing.