Study On Dielectric Relaxation Behavior Of BiFeO₃/Bi_3.25La_0.75 Ti₃O₁₂Film And Dielectric Properties Of Ba(Zr_0.15Ti_0.85)O₃ Ceramic

Dielectric materials with various of kinds and different functions have a wide range of applications. BiFeO₃ with high Curie temperature (TC¹100 K) and high Néel temperature ( TN⁶20 K) is of both ferroelectricity and ferromagnetism, which has potential applications in multifunctional devices. However, the large leakage current hinders its application in the near future. BaTiO₃ ceramic with high dielectric constant and little leakage current is an ideal material for the capacitor devices. But the higher Curie temperature (120℃) limits its application at room temperature.1. Huang Fengzhen etal prepared BiFeO3 (BFO)/Bi_3.25La_0.75Ti₃O₁₂ (BLT) films on Pt/Ti/SiO2/Si substrate via metal organic decomposition (MOD) method. The experimental results demonstrated that BLT film effectively inhabited the leakage current of the BFO layer. And the double films showed dielectric relaxor behavior. In the second chapter of this article, BiFeO3 (BFO) film was considered as relaxor ferroelectric film with a leakage current, and Bi_3.25La_0.75Ti₃O₁₂ (BLT) film was regarded as relaxor ferroelectric film with a leakage current or ferroelectric film with a leakage current. Maxwell- Wagner (M-W) theory had been used to study the dielectric relaxation behavior of BFO/BLT films. Results showed that the characteristics of BFO film significantly affect the dielectric relaxation behavior of the BFO/BLT film. The theoretical results were in good agreement with the experimental data when the temperature was above 400K. It was inferred that the polycrystalline orientation of BLT film and the diffusion of Fe²⁺irons in it lead to the presence of disorganized polar nanoregions (PNRS) in this film, The relaxation characteristics of which was inhibited at low temperature; The polycrystalline orientation of BFO film lead to the presence of PNRs in BFO film, And the relaxation characteristics of it was exhibited at high temperatures.2. In the third chapter of this article, Barium zirconium titanate Ba(Zr_0.15Ti_0.85)O₃(BZT) ceramic was prepared by the traditional solid state reaction. The crystalline structure, microstructure and dielectric characteristics of BZT were measured. It was found that BZT showed dielectric characteristics of diffuse phase transition and relaxation. while for pure BaTiO₃ ceramic, no the dielectric characteristics were observed. Smolenski theory was used to interpret the characteristic of diffuse phase transition. Integrated with the Debye relaxation theory, the frequency dependence of maximun of dielectric constant had been studied. The theoretical results agreed well with the experimental data. At the same time, the Arrhenius relation was used to analyze the relaxation of BZT at high temperature. The result indicated that it was induced by oxygen vacancy.