Hydrothermal Synthesis And Characterization Of The Perovskite Niobates

There has been a great deal of interest and studies in perovskite materials, due to their interesting electrical, magnetic and catalytic properties, and applications in colossal magnetoresistance, magnetocaloric effect and ferroelectricity. The researches mainly focus on two aspects: (1) canons doping in perovskite materials, (2) and creating oxygen vacancies.Hydrothermal synthesis is the process which makes the reactants to the products in the sealed the system in certain temperature with the medium: water. Under this condition, the physical and chemical properties of the substances will change. In this process water has two functions: one is to provide the pressure and the other is to provide a uniformly reaction environment, which makes some difficult reaction react in a mild temperature. Owe to the low reaction temperature some products have different structures and properties. In the solid state chemistry, perovskite structure consists of one of the most basic and the most important structure and the complex oxides with the perovskite structure and the related structures have a bright future in application. So many people are interested in the synthesis, structure and properties.In this paper, we systematically investigate the application of the hydrothermalsynthesis of the complex oxides with the perovskite and other related structures. To some solid state oxide electrolyte synthesized by other methods such as high-temperature solid state reaction, the co-precipitation method and sol-gel methods, we try to get these oxides by more moderate methods, such as the hydrothermal method in order to investigate the difference of the structures, compositions and the properties among these synthesis methods. So we can recognize the relationship between the synthesis and the composition, the structure and the properties of the materials. This is the most important in the directional synthesis of the materials.1.one feature of the hydrothermal synthesis is easy to prepare compounds of the mixed valence and high valence, the adulteration of crystallite material has effects on valence,properties,size and so on. Therefore , we try to synthesize the mixed valence of niobium oxide in hydrothermal conditions, which will help us find the rule of controlling the properties by synthesis. This is the most important in the directional synthesis of the materials.2. Oxide powder usually in 1200℃prepared under high temperature conditions, whether we could decrease the synthesis temperature is meaningful to synthesize some new compounds and explore the synthesis mechanism. The system of KxNa1-xNbO3 has excellent piezoelectric properties, so we try to use the method of hydrothermal synthesis in the system of K-Na-Nb-O.3. BiFeO₃ has a simple perovskite structure. The oxygen octahedron around diagonal axis of rotation angle, the formation of a deviation from ideal perovskite structure of the ramp hexahedron structure. BiFeO3 is one of the very few multiferroics with a simultaneous coexistence of ferroelectric and antiferromagnetic order parameters in perovskite structure, has attracted much attention . Curie temperature(Tc) is 1110K and Nier temperature (Tn) is 650K.The products of solid-state reaction often contain impurities, hydrothermal method can make up for this shortfall.Through our work we get some results as below: 1. We insert two ions Ba2+ and K+ in the location A of perovskite ABO3 by hydrothermal synthesis, we get duplicate mixed valence K0.8Ba0.2NbO3. Recently we have shown that BaNbO3^x ceramic compounds, with perovskite cubic structure and large oxygen nonstoichiometry (0.6