Synthesis And Characterization Of New Layered Perovskite Phases

Layered perovskite oxide is an important functional materials which has many interesting properties such as superconductivity,colossal magnetoresistance, ferroelectricity and photocatalytic activity.In this paper,we reported that several new layered perovskite oxides have been successfully synthesized and characterized.1.Synthesis and characterization of a new two-layer Ruddlesden-Popper perovskiteA new two-layer Ruddlesden-Popper phase Li₂CaTa₂O₇ has been synthesized for the first time.The detailed structure determination of Li₂CaTa₂O₇ performed by powder X-ray diffraction(XRD) and electron microscopy(ED) shows that it crystallizes in the space group Fmmm[a～5.5153(1),b～5.4646(1),c～18.2375(3)(?)]. UV-visible diffuse reflection spectrum of the prepared Li₂CaTa₂O₇ indicates that it had absorption in the UV region.The photocatalytic activity of the Li₂CaTa₂O₇ powders was evaluated by degradation of RhB molecules in water under ultra visible light irradiation.The results showed that Li₂CaTa₂O₇ has high photocatalytic activity at room temperature.Therefore,the preparation and properties studies of Li₂CaTa₂O₇ with a two-layer Ruddlesden-Popper structure suggest potential future applications in photocatalysis.2.Synthesis and characterization of a new four-layer Aurivillius perovskiteA new four-layer Aurivillius phase Bi₂SrNa₂Nb₄O₁₅ has been synthesized by solid state reaction of Bi₂SrNb₂O₉ and NaNbO₃ at 1100℃.The detailed structure determination of Bi₂SrNa₂Nb₄O₁₅ performed by powder X-ray diffraction(XRD) shows that it crystallizes in the space group 14/mmm[a～3.9021(1)(?), c～40.7554(10)(?)].Protonated form of Bi₂SrNa₂Nb₄O₁₅ was obtained by the substitution of bismuth oxide sheets with protons via acid treatment.The conversion into the protonated forms was achieved easily using 6M HCl at room temperature. Preservation of the structure of the perovskite-like slabs and contraction in the c axis were confirmed by X-ray analysis.The compositions of the resulting products were determined to be H_1.8[Sr_0.8Bi_0.2Na₂Nb₄O₁₃]by X-ray fluorescence spectroscopy(XFS) and thermogravimetry.We also successfully synthesized 2+1 layered Aurivillius phase Bi₅Nb₃O₁₅ and Bi₄LaNb₃O₁₅.XRD studies indicated that they are all layered perovskite.3.Crystal Structure of a three-layer Dion-Jacobson phase RbCa₂Nb₃O₁₀ and its protonated formThe Crystal structure of a three-layer perovskite Dion-Jacobson phase RbCa₂Nb₃O₁₀ was investigated through powder X-ray analysis and selected-area electron diffraction observation.The niobate crystallized in the tetragonal system P4/mmm with unit cell parameters a=3.8589(1) and c=14.9120(2)(?).The powder X-ray studies indicated the H-form niobate HCa₂Nb₃O₁₀ had tetragonal symmetry with a=3.8571(14) and c=14.4086(39)(?).HCa₂Nb₃O₁₀ undergoes a topochemical dehydration reaction to make a new metastable phase,Ca₄Nb₆O₁₉,which partly decomposes to microcrystalline CaNb₂O₆ at 600℃.4.The synthesis and characterization of a new two-layer Dion-Jacobson perovskiteA new two-layer Dion-Jacobson phase LiLaNb₂O₇ has been synthesized for the first time.We design a new ion-exchange reaction under low temperature to obtain CuO/LiLaNb₂O₇ composite.The detailed structure determination of LiLaNb₂O₇ performed by powder X-ray diffraction(XRD) and electron microscopy(ED) shows that it crystallizes in the space group P4₂/mcm[a=5.4873(1),c=20.3740(3)(?)]. Therefore,the preparation and structure studies of CuO/LiLaNb₂O₇ composite suggest potential future applications in photocatalysis.By these experiments,we reported that the successful synthesis and characterization of several new layered perovskite oxides which had potential application in the photocatalytic field.