| The complex fluorides with its unique optical, electrical and magnetic propertieshave attracted the attention of scholars and industry. Many synthetic methods havebeen used in the synthesis process for fluorides, among all synthetic methods,hydrothermal process is widely used with a variety of advantages such as mildreaction environment, highly crystalline and high purity products preparing, et al. Butin the classic complex fluorides hydrothermal reaction route before, excessive amountof HF was added as mineralizer. Due to the HF acid is strong corrosive and highlytoxic, considerable dangers in this kind of experiments are existed. The operatorshould be well trained and protected in the whole process, but still cannot completelyavoid the potential threat. The excessive HF addition must lead to excessive F residuein wastewater after reaction. Due to fluoride in drinking water may lead a chronictoxic, such as effect in teeth, bones, soft tissues, brain, neurotransmitter, teratogenesisand cancer, et al. So to find a new reaction route to replace the massive HF added pathhas a great significance in environmental protection.Modern scientific research shows that the performance of the materials and itsmicrostructure is an important relationship, material microstructure on its in optics,electricity, magnetism, et al. have important influence. A lot of physical and chemical processes occur at the surface of the materials; as a result, the surface of the crystalatomic structure is a critical factor affecting the properties of materials. Due to thepresence of high-density atomic steps and edges and abundant unsaturatedcoordination sites, micro-and nanocrystallites with high-energy surfaces usuallyexhibit greater reactivity than those with low-energy surfaces. But under the conditionof the general, the high energy crystal face will disappear in the process of crystalgrowth as the total surface energy is minimized. High-energy crystal facet tailoring ofexisting compounds, which is great significance in the aspect of material preparation,can modify or find new physical and chemical properties. Fluoride has many excellentperformances, such as high resistivity, anionic conductivity and electron-acceptorbehavior. Perovskite fluoride not only has the general performances of fluoride, butalso has some interesting performances, resulting in the outstanding applications ofphotoluminescent and magnetism et al. So the experimental on perovskite typeKMF3fluorides crystal facet tailoring seems to be meaningful.The motivation of this dissertation is to find a new reaction route to instead thethe massive HF acid added path for preparing the cryolite fluorides and tailoring thecrystal facet on perovskite type KMF3fluorides.Our research group has long-term synthesis experience in perovskite compounds,A variety of transition metal oxides with perovskite-type structure were synthesizedby hydrothermal synthesis method. Worthy of attention of our project is ahydrothermal and molten alkali method synthesis perovskite oxide La1-x-yCaxKyMnO3single crystal and thin film samples process with K, Ca co-doped, and the relevantelectrical and magnetic properties on it. But still cannot understand the full properitiesof our sample, so, it is important to adopt the new test and research methods from other point of viow for the stady of La1-x-yCaxKyMnO3sample.1. In the case of a new synthetic route without added HF acid as mineralizer, twokinds of cryolite-type complex fluorides β-Li3VF6and Na3VF6has been prepared in amild hydrothermal method in one step. Highly crystallinity and purity crystal areobtained. In the aspect of synthesis, we make a detailed discussion on the the selectionof raw materials, the pH value in system and filling degree may cause influence on thereaction conditions. To get the optimum ratio for obtain highly purity products.Weanalyzed the fluorine residue in detail with the comparison of the reaction route toNa3VF6and the route in the past. XPS data and magnetic properties were carried outdetailed analysis and quantitative computation for both β-Li3VF6and Na3VF6. For thefirst time declared the binding energy of V3+in the cryolite-type fluoride is517.8eV,higher than the binding energy in other vanadium oxides or vanadium halides between514.1eV to517.2eV. This is mainly due to the higher electronegativity in F than in Oor other halogen. The magnetic property of β-Li3VF6was not been reportedpreviously, with the Curie constant C=1.165cm3Kmol-1, Weiss constantθ=-68K,effective moment μeff=2.76μeff/μBwhich is very close to the value of spin-only stateV3+(2.828μeff/μB). Then we got the effective moment2.23μBfor Na3VF6obtained byus and make a contrast with the reported before. Because of the more distortiondegree, minor V-F-Na bond was presented.2. We synthesized perovskite KMF3(M=Mg, Mn, Co, Ni, Zn) successfully byhydrothermal method, and make a crystal facet tailoring on KMF3by introducing thelarge NH4+ion, a series with different morphology of perovskite-type KMF3(M=Mg,Mn, Co, Ni, Zn) fluoride samples were received. This is mainly due to NH4+when theion accumulation to a certain extent in concentration, the NH4+may occupy the place of K+in the process of KMF3growth. Because of the tetrahedral configuration ofNH4+was differ to K+, It is possible to limit the KMF3cube crystal in corner or edgedirection growth process, Resulting in a cube corner cutting or edge cutting of crystal.3. For mixed valence state perovskite type manganese oxides La1-x-yCaxKyMnO3with hydrothermal synthesis method, magnetic resistance and Hall effect the electricalmagnetic testing and discussion are given here. The diversity of the electricalproperties of samples and the corresponding explanation to the La1-x-yCaxKyMnO3sample are also given. And the La1-x-yCaxKyMnO3were also treated in an appliedelectric field and magnetic field for magnetic testing, other similar samples are testedin the same method for comparison, Unique properties are found in La1-x-yCaxKyMnO3sample and the possible reasons which may involved it were detailed analysis anddiscussion. |
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