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Hydrothermal Synthesis and Characterization of the A、B Site Doped Rare Earth Manganites

Author: ZhouCuiFen
Tutor: FengShouHua
School: Jilin University
Course: Inorganic Chemistry
Keywords: doped perovskite manganites hydrothermal synthesis
CLC: O614.33
Type: Master's thesis
Year: 2010
Downloads: 83
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Abstract


Inorganic Hydrothermal synthesis is an important branch of synthetic chemistry. Hydrothermal synthesis was used to explore the generation of Geology and Mineral Resources at first, now this method that can be used to synthesize zeolite and crystal materials has experienced 100 years of history. Hydrothermal synthetic chemistry is to study reaction laws and mechanism of the material with in the high temperature and pressure conditions. The difference between hydrothermal synthesis and solid-state synthesis is reaction mechanism. The solid- state reaction mechanism is mainly interface diffusion as the medium, and the hydrothermal synthesis is characterized by liquid phase reaction.In general, material sources are related to the micro-structure and properties of materials, and therefore the different "genes" will be obtained by the different synthetic systems and methods .Hydrothermal synthesis focus on the preparation of specific compounds and materials in solvents. What’s more, the merterials can be obtained by hydrothermal method under mild reaction conditions, which can’t be prepared solid-state methods .In recent decades, it is very general for the application of hydrothermal synthesis method to develop advanced materials. The nano-crystallines were synthesized by hydrothermal synthesis with particle size uniformity, small agglomeration , high-crystallinity etc. In addition, synthesis of TiO2 nano-materials by hydrothermal method has been recognized as a classic approach. Metastable state compounds such as organic-inorganic hybrid materials, and complex fluorides, complex oxides are mostly prepared with in hydrothermal environment. At present, this moderate low-temperature synthetic route has recently been investigated extensively. The perovskite-type compounds can be modulated structure, composition, properties of the compound. Both nano-particles and large single crystal can be prepared. Hydrothermal synthesis provides technical support to study nature of compounds.In this paper, we have successfully prepared R1-xAxMnO3, RMn1.5Fe0.5O5 compounds and determined the optimal reaction conditions. Hydrothermal method have advantages because complex perovskite manganese oxides can obtained taking the advantages of simple handed hydrothermal method, which used synthesized by high temperature and high oxygen pressure.Y-doped rare earth manganates R1-xYxMnO3 with stable Orthorhombic structure were obtained by mild hydrothermal synthesis for the first time. Through the control of hydrothermal reaction conditions to selectively synthesis of non-centrosymmetric hexagonal structure (space group P63cm) and Orthorhombic structure R1-xAxMnO3. And the single crystals could be easily grown for Y doping levels 0≦x≦1. Powder X-ray diffraction, scanning electron microscopy and magnetic susceptibility data have been recorded for characterization of all the black products. particle size of single crystal 150-200μm. Temperature depended magnetic susceptibility curves for R1-xYxMnO3 displayed antiferromagnetic property.A series of RMn1.5Fe0.5O5 compounds were synthesized under mild hydrothermal conditions for the first time. And these compounds can usually be prepared under conditions of high oxygen pressure, and the crystal purity is accompanied by impurities. Our study further illustrates the advantages of hydrothermal synthesis. Mn cation at B site of RMn2O5 compounds were substituted with Fe. It is found that RMn1.5Fe0.5O5 was easily obtained with doping levels x≦0.5, while two kinds of compounds RMn1.5Fe0.5O5 and RFeO3 will generate at the levels x≥0.5. And RMn1.5Fe0.5O5 has the same crystal structure as well as the parent compound.

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CLC: > Mathematical sciences and chemical > Chemistry > Inorganic Chemistry > Metal elements and their compounds > Section III group metal elements and their compounds > Lanthanides ( rare earth elements )
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