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 Li_2CaTa_2O_7 has been synthesized for the first time.The detailed structure determination of Li_2CaTa_2O_7 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 Li_2CaTa_2O_7 indicates that it had absorption in the UV region.The photocatalytic activity of the Li_2CaTa_2O_7 powders was evaluated by degradation of RhB molecules in water under ultra visible light irradiation.The results showed that Li_2CaTa_2O_7 has high photocatalytic activity at room temperature.Therefore,the preparation and properties studies of Li_2CaTa_2O_7 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 Bi_2SrNa_2Nb_4O_(15) has been synthesized by solid state reaction of Bi_2SrNb_2O_9 and NaNbO_3 at 1100℃.The detailed structure determination of Bi_2SrNa_2Nb_4O_(15) 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 Bi_2SrNa_2Nb_4O_(15) 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_(0.8)Bi_(0.2)Na_2Nb_4O_(13)]by X-ray fluorescence spectroscopy(XFS) and thermogravimetry.We also successfully synthesized 2+1 layered Aurivillius phase Bi_5Nb_3O_(15) and Bi_4LaNb_3O_(15).XRD studies indicated that they are all layered perovskite.3.Crystal Structure of a three-layer Dion-Jacobson phase RbCa_2Nb_3O_(10) and its protonated formThe Crystal structure of a three-layer perovskite Dion-Jacobson phase RbCa_2Nb_3O_(10) 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 HCa_2Nb_3O_(10) had tetragonal symmetry with a=3.8571(14) and c=14.4086(39)(?).HCa_2Nb_3O_(10) undergoes a topochemical dehydration reaction to make a new metastable phase,Ca_4Nb_6O_(19),which partly decomposes to microcrystalline CaNb_2O_6 at 600℃.4.The synthesis and characterization of a new two-layer Dion-Jacobson perovskiteA new two-layer Dion-Jacobson phase LiLaNb_2O_7 has been synthesized for the first time.We design a new ion-exchange reaction under low temperature to obtain CuO/LiLaNb_2O_7 composite.The detailed structure determination of LiLaNb_2O_7 performed by powder X-ray diffraction(XRD) and electron microscopy(ED) shows that it crystallizes in the space group P4_2/mcm[a=5.4873(1),c=20.3740(3)(?)]. Therefore,the preparation and structure studies of CuO/LiLaNb_2O_7 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.