engleski

Ba4Ta2O9 Oxide Prepared from an Oxalate-Based Molecular Precursor—Characterization and Properties

A novel heterometallic oxalate-based compound, {; ; ; Ba2(H2O)5[TaO(C2O4)3]HC2O4}; ; ; •H2O (1) was obtained by using an (oxalato)tantalate(V) aqueous solution as a source of the complex anion, and characterized by the X-ray single-crystal diffraction, IR spectroscopy, and thermal analysis. Compound 1 is a three-dimensional (3D) coordination polymer with the Ta atom connected to eight neighboring Ba atoms through the oxalate ligands and the oxo-oxygen group. Thermal treatment of 1 up to 1200 °C leads to molecular-to-materials conversion that yields the mixed-metal γ-Ba4Ta2O9 phase. This high-temperature γ-Ba4Ta2O9 polymorph has the 6H-perovskite structure (space group P63/m), in which the Ta2O9 face-sharing octahedral dimers are interconnected via corners to the regular BaO6 octahedra. To date, γ-Ba4Ta2O9 has never been obtained at room temperature (RT), because of the reduction of symmetry (P63/m → P21/c) that usually occurs during the cooling. Spectroscopic, optical, photocatalytic and electrical properties of the obtained γ-Ba4Ta2O9 phase were investigated. In addition to the experimental data, an absorption spectrum and bandstructure of the γ-Ba4Ta2O9 polymorph were calculated using the density functional theory.

Ba4Ta2O9; oxalate-based complex; crystal structure; Rietveld refinement; photocatalyst; density functional theory; electrical conductivity

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