Study On The Synthesis And Dielectric Characteristics Of Microwave Dielectric Ceramic Material Co_0.5Ti_0.5NbO₄

With the rapid development of electronic information technology,microwave technology plays an important role in modern communications,national defense and other fields,whether in the field of 5G communication or military radar,microwave devices are gradually developing towards miniaturization and high integration.Low-temperature co-fired ceramic（LTCC）technology uses ceramic materials as substrate media,which greatly improves the integration and reliability of circuits.LTCC microwave dielectric ceramics used in base stations and radar need to have a low sintering temperature to meet LTCC application requirements in addition to medium-high dielectric constant,low dielectric loss,and near-zero resonant frequency temperature coefficient.Based on this,this thesis selects Co_0.5Ti_0.5Nb O₄ with tetragonal rutile structure as the research object,first explores the optimal process parameters for the synthesis of pure phase through experiments,then reduces the sintering temperature by doping three sintering additives（LBSCA,LMZBS,H₃BO₃）,and finally adjusts the resonant frequency temperature coefficient by composite La Al O₃ and Zn Ti Nb₂O₈ on the basis of sintering.The specific work is as follows:The temperature at which the phase transition occurs during calcined of Co_0.5Ti_0.5Nb O₄ was explored,and a single rutile structure Co_0.5Ti_0.5Nb O₄ was obtained when pre-firing above 1140°C.The effect of sintering temperature on Co_0.5Ti_0.5Nb O₄ bulk density and grain defects was analyzed,and it was found that its dielectric properties were mainly related to body density,and CTN ceramics sintered and kept at 1225°C for 6h had the best dielectric properties,and theirε_r=61.4,Q×f=8023Ghz,τ_f=162ppm/°C.Two kinds of low melting glass（LBSCA,LMZBS）and one oxide（H₃BO₃）were selected to reduce the sintering treatment of Co_0.5Ti_0.5Nb O₄,and the results were as follows:（1）XRD and Rietveld finishing results showed that doping LBSCA would lead to the generation of the second phase Co Nb₂O₆,and the proportion of Co Nb₂O₆gradually decreased with the increase of doping amount,and the dielectric constantsεr and Q×f of Co_0.5Ti_0.5Nb O₄ ceramics were affected by density,Grain size,grain defects,effects of second phase.The temperature coefficient is closely related to the proportion of the second phase.Doped LBSCA can greatly reduce the densification sintering temperature of Co_0.5Ti_0.5Nb O₄,and finally the Co_0.5Ti_0.5Nb O₄-0.9wt.%LBSCA ceramics sintered at950°C have excellent dielectric properties,and theirεr=54.1,Q×f=10353Ghz,τ_f=172.157ppm/°C.（2）XRD analysis and Rietveld refinement results show that the doping of LMZBS in Co_0.5Ti_0.5NbO₄ will produce the second phase Co Nb₂O₆,and the proportion of Co Nb₂O₆ increases with the increase of LMZBS doped.The dielectric constantsεr and Q×f of Co_0.5Ti_0.5Nb O₄ ceramics are mainly affected by density,sintering temperature,and second phase,and the temperature coefficient is related to the mass fraction of Co Nb₂O₆,the doping of LMZBS can make Co_0.5Ti_0.5Nb O₄ ceramics reach saturation sintering at1025°C,and finally the Co_0.5Ti_0.5Nb O₄-2wt.%LMZBS ceramics sintered at 1025°C have excellent dielectric properties,and theirεr=55.21,Q×f=9428Ghz,τ_f=208.783ppm/°C。（3）Doping H₃BO₃ in Co_0.5Ti_0.5Nb O₄ ceramics will not cause phase changes,the introduction of H₃BO₃ greatly affects the densification sintering temperature of Co_0.5Ti_0.5Nb O₄ ceramics,Co_0.5Ti_0.5Nb O₄ ceramics sintered at 1150°C and 1200°C can achieve densification sintering when the doping amount is 2wt.%,while Co_0.5Ti_0.5Nb O₄ceramics sintered between 950°C and 1100°C in the lower temperature range need to increase the doping amount to 4wt.%to achieve densification.Its dielectric properties are mainly affected by the acceptor density,and finally the Co_0.5Ti_0.5Nb O₄-4wt.%H₃BO₃ceramic sintered at 1100°C achieved excellent dielectric properties,itsεr=61.59,Q×f=8270 GHz,τ_f=177.431ppm/°C.Two materials with large negative temperature coefficients（LaAlO₃ and ZnTiNb₂O₈）were used to recomposite with the burned ceramics sequentially to adjust their resonant frequency temperature coefficient.The experimental results show that:（1）After the sintering,all La Al O₃reacts with Zn Ti Nb₂O₈ to generate La Ti Nb O₆（τf=69.7ppm/°C）,and finally,0.6Co_0.5Ti_0.5Nb O₄-0.4La Al O₃-0.9wt.%LBSCA sintered at1050°C has good dielectric properties,itsεr=37.6,Q×f=6270GHz,τ_f=121.162ppm/°C.（2）After（1-x）Co_0.5Ti_0.5Nb O₄-x Zn Ti Nb₂O₈ composite ceramics were doped with0.5wt.%LBSCA sintering,only trace amounts of Co_0.5Ti_0.5Nb O₄ were retrieved when x=0.6,and the remaining doped components formed solid solution（Zn,Co）Ti Nb₂O₈.0.2Co_0.5Ti_0.5Nb O₄-0.8 Zn Ti Nb₂O₈-0.5wt.%LBSCA composite ceramics sintered at950°C for 6h have achieved good dielectric properties,and theirεr=36.19,Q×f=36974Ghz,τ_f=-62.137ppm/°C are expected to be used in LTCC fields after improvement.