Research Of Microwave Dielectric Properties Of MgTiO₃-SrTiO₃with High Quality Factor

With the rapid development of radar technology and microwave communication, theresearch of microwave dielectric resonator materials was developed to microwavehigh-end direction. MgTiO₃ceramic is one of the typical microwave dielectric ceramicsystems with high quality factor, which is the microwave dielectric ceramic withexcellent microwave dielectric properties. However, MgTiO₃ceramic still has problemssuch as low dielectric constant, negative temperature coefficient of resonant frequency,high sintering temperature, which limits its application. We reduce the sinteringtemperature and furthermore optimize the excellent microwave dielectric properties bysubstituting the A-site ionic for MgTiO₃-SrTiO₃ceramic in this dissertation.（1-x）MgTiO₃-xSrTiO₃（MST，x=0⁰.065mol） microwave dielectric ceramics wereprepared by solid sate reaction technique, added low melting point oxides as sinteringaids and dopant and substitute on the A-site. The influence of sintering properties, phasecomposition, microstructure and microwave dielectric properties of MST systemmicrowave dielectric ceramics with different content of sintering additives and dopingion was studied.The results show that MgTiO₃-SrTiO₃do not form a solid solution with in the scopeof studied compositions, but mainly to MgTiO₃crystal phase, SrTiO₃crystalline phase,and with the increase of x, the middle phase of MgTi₂O₅diffraction peak graduallyweaken. At the same time，the bulk volume density, the dielectric constant εrandtemperature coefficient of resonant frequency τfincrease, but quality factor and resonancefrequency Q×f value of the product decrease. As the x=0.035mol, the ceramic sintered at1380℃for2h exhibits near-zero temperature coefficient of resonant frequency: τf=-2.8×10-6/℃, high quality factor:Q×f=16714GHz and dielectric constant εr=21.5.0.965MgTiO₃-0.035SrTiO₃（MST） microwave dielectric ceramic was prepared bysolid state reaction method. Zn2+was selected to cooperated into the A-site of965MSTceramic, and the effect of Zn2+doping amount on sintering behavior, phase composition,microstructures and microwave dielectric properties of the ceramic was investigated. Theresults showed that the incorporation of Zn2+promoted the sinterability and improved thedensity significantly. The main crystal phases were not changed. The dielectric constantof the ceramic increases while the quality factor and frequency temperature coefficientdecrease slightly with the increase of Zn2+doping amount. The diffraction peak intensityof intermediate phase MgTi₂O₅gradually decreases to completely disappear with Zn2+doping. When the Zn2+doping amount y=0.03, the sintering temperature of MST ceramicreduced from1380℃to1290℃, and excellent microwave dielectric properties were as follows: εr=22.51, Q×f=16689GHz, and τf=-4.52×10-6/℃.0.965MgTiO₃-0.035SrTiO₃（MST） microwave dielectric ceramics doped with Co₂O₃（1.5⁵.0wt%） were prepared by traditional electronic ceramic technique, the influencesof the content of Co₂O₃on sintering characteristics, phase compositions, microstructuresand dielectric properties of MST microwave ceramics were studied. The results of theresearch indicate that the main crystal phase of the MST ceramic is MgTiO₃and thesub-crystal phase is SrTiO₃.The bulk density of the ceramic increased, which indicatesthat the sintering degree of MST ceramic is promoted by doping Co₂O₃. The dielectricconstant of ceramic decreased slightly, temperature coefficient of resonant frequency andquality factor of the ceramics increase, the middle phase of MgTi₂O₅diffraction peakdecreases gradually to disappear completely with the increase of Co₂O₃dopant. As theaddition of Co₂O₃is3.0wt%, the sintering temperature of MST ceramic reduces from1380℃to1290℃, exhibiting excellent microwave dielectric properties: temperaturecoefficient of resonant frequency τf=-2.53×10-6/℃, high quality factorQ×f=19006GHzand dielectric constant εr=20.5.