Microstructure,Electrical And Photocatalytic Properties Of Bi₅Ti_3-xFe_1+xO₁₅ Four-layer Perovskite Oxide Containing Bismuth

In recent years,the integration of industrial technologies in multiple fields has promoted theexploration of new functional materials,which has led people to pay more attention to the attention and research of multi-functional materials while continuously improving existing technologies.In the field of new material technology,people’s understanding of the relationship between material microstructure and performance is deepening,which further broadens the scope of material applications.At the same time,the multiple uses of materials in different fields have in turn prompted scientists to further explore their microstructure and reaction mechanisms.Bismuth containing layered perovskite oxide materials have unique electrical and photocatalytic properties,which make them attractive in the fields of low loss,high storage information technology,and photocatalytic degradation.In this thesis,the electrical and photocatalytic properties of the four-layer perovskite oxide Bi₅Ti₃Fe O₁₅ matrix material were optimized and improved from both structural and morphological aspects by adjusting the proportion of Fe³⁺and Ti⁴⁺ions at the B position to partially replace Ti⁴⁺at the B position.The main work and achievements of this paper are as follows:（1）Six groups of powder samples of Aurivillius phase four-layer perovskite Bi₅Ti_3-xFe_1+xO₁₅（BTF-x,x=0,0.2,0.4,0.6,0.8,1）were synthesized by molten salt method.The samples were characterized by X-ray diffraction（XRD）,scanning electron microscopy（SEM）,X-ray energy dispersive spectroscopy（EDS）,ultraviolet visible absorption spectroscopy（UV-vis）,and Raman spectroscopy.Using Rietveld to refine XRD,it was found that the adjustment of the proportion of Fe³⁺and Ti⁴⁺ions changed the crystal cell parameters of the matrix material,and the increase of Fe³⁺content significantly reduced the crystal cell size.x=1 had a minimum crystal cell volume of 1035.58?.XRD and Raman spectroscopy results showed that the adjustment of the proportion of Fe³⁺and Ti⁴⁺ions did not change the crystal structure of the matrix material Bi₅Ti₃Fe O₁₅.The microscopic morphology of this series of layered perovskite powders is sheet like particles,with an optical band gap value of 2.1 e V to 2.5 e V,and the band gap gradually narrows as the Fe³⁺/Ti⁴⁺ratio increases.Powder samples were used as photocatalysts to degrade Rhodamine B（Rh B）under visible light,and the photocatalytic activity of the samples was studied and evaluated.The test results show that increasing the concentration of Fe³⁺at the B site can improve the photodegradation efficiency of the Bi₅Ti₃Fe O₁₅ sample,where the Bi₅Ti₂Fe₂O₁₅ with x=1 has the highest photodegradation efficiency,and the first order kinetic constant k=0.14168 min^-1.This work provides a foundation and a stable and effective synthesis method for the further development of new visible light photocatalysts,as well as an optimization idea for using Aurivillius layered perovskite as a visible light catalyst to improve its degradation efficiency.（2）BTF-x（x=0,0.2,0.4,0.6,0.8,1）ceramics were synthesized by molten salt method and their electrical properties were studied.According to the fitting results of electrical modulus and DC conductivity in the low temperature range,it can be seen that dielectric relaxation is caused by oxygen vacancies.The fitting results of DC conductivity in the high temperature range show that the conductive mechanism in the high temperature range is electronic conductivity,which is basically consistent with half of E_g.The ferroelectric test results show that the increase in the Fe³⁺/Ti⁴⁺ratio effectively increases the coercive field,residual and saturation polarization strengths,while reducing the leakage current,resulting in better insulation performance.（3）Six groups of powder samples of BTF-x（x=0,0.2,0.4,0.6,0.8,1）were prepared by hydrothermal method.The effects of hydrothermal reaction conditions and changes in Fe³⁺/Ti⁴⁺ratio on the morphology of BTF-x were studied.Due to the excellent photocatalytic activity and stability of Aurivillius four-layered perovskite oxide Bi₅Ti₃Fe O₁₅ containing bismuth,this section continues the previous chapter’s idea of optimizing its photocatalytic performance by changing the Fe/Ti ratio of layered perovskite Bi₅Ti₃Fe O₁₅ at the B position.Based on the morphology control,the ratio of Fe³⁺and Ti⁴⁺ions at the B site was adjusted to further optimize the photocatalytic performance.Among them,Bi₅Ti₂Fe₂O₁₅ with x=1 had the highest photocatalytic efficiency,and the first order kinetic constant k=0.40941 min^-1.Nanoflower morphology samples were successfully prepared by hydrothermal method,which solved the problems of high reaction temperature（usually higher than 800℃）and cumbersome preparation process in the molten salt process.