Effects Of SrO-B₂O₃-SiO₂Glass Additive On The Dielectric Properties Of Ba_xSr_1-xTiO₃-based Ceramic

With the development of new energy systems, hybrid electric vehicleinverter devices and the demand for low cost and miniaturization of powerelectronic systems, future technological advances will depend on advances indielectric materials with high power and energy densities. In this thesis, theeffects of Kaolinite, SrO-B2O₃-SiO₂glass additive and Zr⁴⁺ion doping on thedielectric properties of Ba_xSr_1-xTiO₃-based ceramics were investigated. It aimedto further improve the breakdown strength of ceramic on the premise ofmaintaining a high dielectric constant such that achieves a higher energy density.Kaolinite was employed as sintering aid to reduce the sintering temperatureof BaTiO₃ceramics. The addition of Kaolinite significantly lowered the sinteringtemperature of BaTiO₃ceramics to¹200℃. XRD results show BaTiO₃ceramics with a low amount of Kaolinite exhibited perovskite structure, while10.0wt%Kaolinite additions resulted in the formation of a secondary phase,BaAl2Si2O8. BaO-TiO₂-Al2O₃-SiO₂glass was formed and improved averagebreakdown strength of ceramics. The Kaolinite content had shown a stronginfluence on the dielectric constant and diffuse transition. BaTiO₃ceramic with4.0wt%Kaolinite addition possessed well temperature stability of dielectricconstant.SrO-B2O₃-SiO₂glass powders were prepared and employed as sintering aidsto reduce the sintering temperature of Ba_0.4Sr_0.6TiO₃ceramics. The effects ofglass content and sintering temperature on the densification, dielectric propertiesand energy storage properties of Ba_0.4Sr_0.6TiO₃ceramics have been investigated.The relative density characterization results indicate densification ofBa_0.4Sr_0.6TiO₃ceramics with glass content becomes apparently from sinteringtemperature of¹060℃. XRD results show all Ba_0.4Sr_0.6TiO₃ceramics exhibit aperovskite structure without the formation of a secondary phase. The dielectricconstant and dielectric loss decreased gradually with increasing glass content. The relationship between dielectric constant and breakdown strength wasdiscussed using the thermochemical model. A discharged energy density of_0.44J/cm³with an energy efficiency of67.4%was achieved for Ba_0.4Sr_0.6TiO₃ceramic with2.0wt%glass addition sintered at1180℃.For further improve the dielectric constant and breakdown strength ofBa_0.4Sr_0.6TiO₃ceramic, Ba_0.4Sr_0.6(Zr_yTi_1-yO₃ceramic was prepared by solid-statemethod. Quantitative SrO-B2O₃-SiO₂glass as sintering aid was introduced tolower the sintering temperature. The effects of Zr⁴⁺content on densification,dielectric constant and breakdown strength of ceramics have been investigated.The sintering temperature of ceramic increased gradually with increasing in Zr⁴⁺content. The dielectric constant and breakdown strength of ceramic increasedfirst and then decreased. While the dielectric loss of ceramic hardly changed. Thetemperature dependence of dielectric loss plot for sample showed a peak, and theposition of this peak changed with Zr⁴⁺content.Considering the high dielectric constant and breakdown strength ofBa_0.4Sr_0.6Zr_0.15Ti_0.85O₃ceramic, the effects of SrO-B2O₃-SiO₂glass on thesintering temperature, dielectric properties, and energy storage properties ofceramic have been investigated. Dielectric breakdown strength of22.4kV/mmwas achieved for Ba_0.4Sr_0.6Zr_0.15Ti_0.85O₃ceramics with20.0wt%glass content.The relationship between dielectric breakdown strength and grain boundarybarrier was studied by the measurements of dielectric breakdown strength andactivation energy. A discharged energy density of_0.45J/cm³with an energyefficiency of88.2%was achieved for Ba_0.4Sr_0.6Zr_0.15Ti_0.85O₃ceramic with5.0wt%glass addition sintered at1240℃.