Synthesis And Properties Of Tantalate Oxyfluoride And Tantalates

Tantalum oxyfluoride anions are key constituents of materials that exhibit important structure-related properties, such as second-order nonlinear optical and dielectric activity,ferroelectricity, and piezoelectricity.The tantalate compounds doped by transition metals are observed to be one of the most promising ways to improve the visible light activity of the wide band gap semiconductor photocatalysts. There has been a growing interest in synthesis and preparation of tantalum oyxfluoride compounds and transition metals doped tantalates.Tantalum oxyfluoride anions are usually constructured to various types of clusters by bridging oxygen atoms of the simple octahedron building blocks Ta F6, in which the major reported frameworks have three types: dimer [Ta2OF10]2-, tetramer [Ta4F16O4]2-and octamer[Ta8F24O12]8-. Their counterions are usually the quaternary ammonium cations or protonated organic amines. The initiation materials for preparing tantalum compounds are tantalum oxide, tantalum pentachloride, tantalum ethoxide. Insoluble tantalum oxide is an inappropriate precursor for solution methods. Tantalum pentachloride and tantalum ethoxide are relatively toxic and moisture sensitive, and incompatible with water-based processing methods. In addition, its halide compounds are scarcely soluble in common solvents, and easily susceptible to hydrolysis by traces of moisture, which makes such materials particularly difficult to handle. The tantalum element is very inert and difficult to react with other reagents except for HF acid or extremely high concentration base to produce the relevant fluoride and hydroxide complexes. In this paper we tried to utilize metal tantalum and aqueous hydrofluoric acid with varied corresponding p H values as thestarting material.Metal-phen complexes are integrated into the tantalum oxyfluoride anions to prepare novel tantalum oxyfluorides, and their structures and optical properties were characterized. The major contents are as follows:Part 1, under two-step hydrothermal condition, four metal-phen functionalized compounds, [Fe(phen)3][Ta2OF10](1),[Fe(phen)3][Ta2OF10]·2H2O(2),[Co(phen)2Cl2][Ta F6](3),[Ru(phen)3]2[Ta2OF10][Ta F6]2(4) are successfully synthesized and characterized by single-crystal analysis. Many kinds of intr-/intra- molecular interactions are found, such asπ???π stacking and C-H???F hydrogen bond contact. These are the first example of introducing the M-phen into the tantalum oxyfluoride anions. The Ru-phen moiety plays an important role in photocurrent response of the compound.Part 2, by quantitative control method, we successfully prepared Fe(Co)-doped tantalate compounds. X-ray powder diffraction show that those compounds maybe the mixture of perovskite and pyrochlore tantalates, and morphology of the Fe(Co)-doped tantalate compounds depends on temperature and time of heat treatment.