Study Of SrBi₄Ti₄O₁₅ Ferroelectric Ceramics And Thin Films

Due to the excellent endurance properties against polarization switching, theBismuth-layered-perovskite oxides such as SrBi₂Ta₂O₉, Bi_4-xLa_xTi₃O₁₂ and SrBi₄Ti₄O₁₅ havegreat potential use in ferroelectric random access memories. SrBi₄Ti₄O₁₅ seems moreinteresting since it has a lower depositing temperature than that of SrBi₂Ta₂O₉, and a betterfatigue endurance than that of Bi₄Ti₃O₁₂, however, the SrBi₄Ti₄O₁₅ without doping showssmall remanent polarization, and the SrBi₄Ti₄O₁₅ films are difficulty to be prepared byliquid-phase method without the appearance of pyrochlore phase (Sr,Bi)₂Ti₂O₇ andmicro-cracks. The relationship between preparation technology and properties of SrBi₄Ti₄O₁₅ceramics, and the relationship between heat treatment technology and crystal structure,morphologies of SrBi₄Ti₄O₁₅ film have been researched systematically.The effect of Bi content on the sintering behavior and microstructural development of SrBi₄Ti₄O₁₅ceramics were studied. It is found that the addition of excess Bi₂O₃ can improve densification ofSrBi₄Ti₄O₁₅ and suppress its decomposition, can suppress the produce of (Sr,Bi)₂Ti₂O₇ and the extrinsicstacking faults. With more Bi₂O₃ addition, the specimens exhibit progressing stronger c-axis orientation.The influences of Ba doping and La doping on SBTi ceramics were studied. For Sr1-xBaxBi4Ti4O15ceramics, with increasing Ba2+ substitution, the Curie temperature, coercive field and permanentpolarization decrease continuously with the increase of Ba content. For Sr0.3Ba0.7Bi4-xLaxTi4O15ceramics, the Curie temperature and coercive field decrease continuously with the increase of La content.The remnant polarization increases at first, then decreases with the increase of La content.The Ag particles were incorporated to the SBTi and the dielectric properties of SBTi/Agcomposites were investigated. It is found that Ag doping can significantly lower the sinteringtemperature of SBTi ferroelectric composites. By increasing Ag content, a gradual increase ofthe dielectric constant is observed when the temperature ranger from room temperature to200°C, however, the Curie peak of dielectric constant is repressed.The stable SBTi precursor solution were prepared using strontium chloride, bismuthnitrate, tetrabulyl titanate as raw materials, and citric acid as complex agent, and ethanolabsolute, water, hydrochloric acid as solvents of tetrabulyl titranate, strontium chloride,bismuth nitrate, respectively.The relationship between heat treatment technology and crystal structure, morphologiesof SrBi₄Ti₄O₁₅ thin film have been researched systematically, and SBTi thin film without theappearance of (Sr,Bi)₂Ti₂O₇ and micro-cracks were prepared by the control of heat treatmenttechnology. It is found that SrBi₄Ti₄O₁₅ thin films are difficulty to be prepared by traditionalcrystallization general thermal annealing method and by traditional crystallization rapidthermal annealing method without the appearance of a pyrochlore phase (Sr,Bi)₂Ti₂O₇ andmicro-cracks prepared, however, SrBi₄Ti₄O₁₅ thin films without the appearance of(Sr,Bi)₂Ti₂O₇ can be prepared easily by layer-by-layer rapid thermal annealing method on Si,Al2O3 and Pt/Ti/SiO2/Si substrates.SrBi4-xLaxTi4O15 thin films on p-Si substrates were prepared by layer-by-layer rapidthermal annealing method. The results show that the growth of SrBi₄Ti₄O₁₅ on bare p-Sisubstrates is c-axis-oriented with the increase of annealing temperature, and the degree ofc-axis orientation reduces with the increase of La content when heat treatment condition wassame. SBTi thin films with enhanced a-axis orientation were prepared on Pt/Ti/SiO2/Sisubstrates by layer-by-layer rapid thermal annealing method. The results indicate that thedegree of a-axis orientation increase with with the increase of layers.