Fabrication And Characterization Of Low-Dimensional Perovskite Nano Oxides

Perovskite oxide can be generally described as AB03 chemical formula,where A-site is usually occupied by alkaline earth ion or rare earth ion and B-site is usually occupied by transition metal ions.The function properties of perovskite oxides come from the offsets of displacements of positive or negative ions.The adulterations of A-or B-site ions result in very abundant physical and chemical properties in perovskite oxides,such as dielectric properties,ferroelectric properties,pyroelectric properties,photoelectric characteristics,photocatalysis properties,superconducting properties and giant magnetoresisive effects etc.As a result,perovskite oxides have been widely applied in different fields of modern industry.BaTiO₃?BTO?and PbTiO₃?PTO?are the typical perovskite oxides.As a typical ferroelectric material,the ferroelectricity of BTO origins from the vibration of the Ti4+ion within the[Ti06]octahedron.As a representive piezoelectric material,PTO greatly extends the working temperature range of perovskite oxides.However,the previous works are focused on the synthesis and characterization of bulk BTO and PTO materials.Due to the microminiaturization of electronic devices and the special properties of low-dimensional oxides,the synthesis and characterization of low-dimensional perovskite oxides have received much attention.Up to now,many methods have been developed to synthesize perovskite oxide materials,such as sol-gel process,microwave hydrothermal process,solid-state method,chemical solution deposition and molten salt method,and etc.Among them,molten salt method has been widely used because of its special advantages,such as the lower reaction temperature and shorter reaction time,easy controllability of the shape and size of products,high purity of products and easy removal process of salts.This thesis reports on the molten salt syntheses and microstructural characterizations of BTO nano particles?OD nanomaterial?,BTO nanorods?1D nanostructure?and PTO 1D nanostructure.The detailed results are described as the followings:The first part is about the molten salt synthesis of BTO particles.In this part,the effects of different annealed temperatures and molten salt ratios on the growth of BTO particles were investigated.The results showed that the sizes of the BTO particles were gradually increased from 320 nm to 1000 nm with increasing the annealed temperature,and the c/a ratios?a and c are lattice parameters of the BTO particle?were also increased from 1.007 to 1.010.While with the increase of molten salt ratios,the morphology of particles gradually became spherical shape from cubic shape and a few rod-like structures appeared.The amount of BaCO₃ impurity of was also increased simultaneously.The dielectric measurements at room temperature show that the dielectric constants of the BTO particles arein the range of 700-1300?@ 1 kHz?,and the corresponding dielectric losses are in the range of 0.01-0.03.The second part is about the synthesis of BTO 1D nanostructures via traditional molten salt method and template molten salt method.In this part,the effects of different reaction conditions?e.g.the types of reactants,molten salt ratios,annealed temperature and soaking time?on the growth of BTO 1D structures were investigated.The results demondtrated that many 1D BTO structures were synthesized by traditional molten salt method at 800? for 5 h and the molar ratios of BaCO₃:TiO2?anatase?:NaCl:KCl equal to 1:1:60:60.The length of rods was about 5?m with a diameter of 130-200 nm and the products showed homogeneous morphology,Large quantity of 1D BTO structures were also synthesized by template molten salt method at 650? with molar ratios of BaC2O4:BaTi2O5 template:NaCl:KCl equal to 1:1:60:60.The products successfully inherited the morphologies of the templates and their length was about 5-10 ?m and the average diameter was about 300 nm.The ultraviolet-visible spectra showed that the optical bandgap of the BTO 1D structures synthesized by molten salt method was about 2.5-2.6 eV,which was much smaller than the corresponding value of traditional bulk BTO materials?3.28 eV?.The third part is about the synthesis of PTO 1D structures by traditional molten salt method and template molten salt method.With the molten salt ratio of NaCl:KCl=30:30,some PTO rods with the length over 50 ?m?diameter?550 nm-2.0 ?m,aspect ratio of 100?were observed.By template molten salt method,some PTO rod structures were synthesized with the length of 3-10 ?m?diameter?1.0 ?m?,and some chain structures connected by small particles appeared,which might reveal the growth mechanism of one-dimensional rod structures.