Investigation On The Dielectric Roperties Of Barium Strontium Titanate-based Ceramics

The development of science and technology come up with a higher demandon the energy storage components. The performance of high voltage, largecurrent and high energy storage density becomes the key for the future energystorage components. In this thesis, the effects of different Sr/Ba ratio andBaO-TiO2-SiO2glass additives on the crystal structures, breakdown strength andenergy storage properties of Ba1-xSrxTiO3ceramics were investigated. At thesame time, Ba1-xSrxTiO3glass-ceramics were prepared by powder sintering andmelt casting. The effects of molding method on the microstructures andbreakdown strength were investigated.The purpose was prepared storagemedium materials with high dielectric constant, low dielectric loss and highbreakdown strength.The Ba1-xSrxTiO3ceramics were prepared by the traditional solid phasemethod, the effects of different Sr/Ba ratio on the microstructures, relaxizationphenomenon and energy storage properties were investigated. The experimentalresults show that the polarization and dielectric constant of Ba1-xSrxTiO3ceramicswere decreased. The Ba1-xSrxTiO3(x=0.5~0.7) ceramics processed parelectricphase at room temperature, which contributed to the gradually decrease ofdielectric loss. The radius of Sr2+was smaller than that of the Ba2+, the latticeparameters of ceramics was reduced, the grain size was refined. The optimizationof microstructure lead to the increase of average breakdown strength of ceramics,the samples ofBa0.4S r0.6TiO3ceramics obtained the highest energy storagedensity of0.36J/cm3. The decrease of grain size resulting in more grainboundaries, more space charge and defects existed at grain boundaries, it wasdifficult for transferring charge and making an orientation under external electricfield. The thermally activated motions of defects were accelerated, leading to theincrease of activation energy.In order to further improve the microstructure, improve the breakdownstrengh and energy storage density ofBa0.4S r0.6TiO3ceramics, the samples with BaO-TiO2-SiO2glass as the sintering additives were prepared. The effects ofglass contents on the sintering behavior and dielectric property of ceramics wereinvestigated. The experimental results show that the BaO-TiO2-SiO2glass wascomposed with BaTi2Si2O8ferroelectric crystal phase and glass phase. The glassphase as the liquid phase during sintering, which reduced the sinteringtemperature of the ceramics, increased the densification, inhabited the growth ofgrain size, the breakdown strength ofBa0.4S r0.6TiO3ceramics with glassaddition were improved remarkably. The breakdown strength of samples with9.0wt%glass addition was16.51kV/mm, which was1.8times of pureBa0.4S r0.6T iO3ceramics. The crystal phase BaTi2Si2O8inhibited the decrease ofdielectric constant ofBa0.4S r0.6TiO3ceramics resulting from the glass phaseaddition. The energy storage density of ceramics was observably increased withthe joint action of crystal phase and glass phase. The samples with5.0wt%glassaddition obtained the energy storage density of0.60J/cm3.The existence of defects such as pore aggravated the breakdown strength ofBa0.4S r0.6TiO3ceramics. The Ba1-xSrxTiO3glass-ceramics were prepared bypowder sintering and melt casting. The effects of molding method on the crystalstructures, microstrues and dielectric properties were investigated. Theexperimental results show that the glass-ceramics prepared by powder sinteringwere consisted of crystal phase and glass phase, which were easier tocrystallization, ferroelectric phases were distributed homogeneous in the glassmatrix. While the glass-ceramics prepared by melt casting were completelyconsisted of glass phase, there were no crystal phases and pore can be observedin the SEM micrograph. The breakdown strength of Ba1-xSrxTiO3glass-ceramicswas significantly greater than the samples prepared by powder sintering. Thebreakdown strength ofBa0.4S r0.6TiO3samples prepared by melt casting was588kV/cm, the dense microstructure of glass phase resulting in the samples obtainedthe highest energy storage density of2.08J/cm3.