Low Temperature Sintering And Properties Control Of Magnesium Titanate Microwave Dielectric Ceramics

With the development of modern communication technology,the demand for relevant components is also increasing.Microwave dielectric ceramics,as a dielectric material applied in microwave frequency circuit,is widely used in the field of mobile communication due to its good microwave dielectric properties,wide application frequency range,low raw material cost and simple preparation process.In recent years,in order to meet the requirements of miniaturization and integration of modern communication tools,people put forward LTCC（Low Temperature co-fired Ceramic）.The emergence of LTCC further increases the application range of microwave dielectric ceramics and reduces the production cost of microwave dielectric ceramics.Magnesium titanate microwave dielectric ceramics are widely used in the market at present,among which Mg Ti O₃ and Mg₂Ti O₄ ceramics have low dielectric constant and high quality factor,which are very suitable as the matrix materials of microwave communication components.However,it has some disadvantages,such as high sintering temperature,poor density,poor stability of frequency and temperature,which seriously hinder its application in microwave components.In view of the shortcomings of Mg Ti O₃ ceramics and Mg₂Ti O₄ ceramics,the method of A/B site ion substitution and adding Li F or Li F-2Ca F₂-2B₂O₃（LCB）as sintering additives was used to improve their sintering performance and control their frequency and temperature stability,and the following research results were obtained:1.Mg Ti O₃ Mg(Ti_0.95Sn_0.05)O₃,(Mg_0.95Ni_0.05)(Ti_0.95Sn_0.05)O₃,and(Mg_0.95Zn_0.05)(Ti_0.95Sn_0.05)O₃ ceramics were prepared by using Sn⁴⁺to replace Ti⁴⁺and Ni²⁺and Zn²⁺to replace Mg²⁺,and studied the change of sintering properties and microwave dielectric properties of the samples.The results show that the main phase of the samples sintered at 1275°C is Mg Ti O₃,accompanied by the formation of trace Mg₂Ti O₄.Mg Ti O₃ ceramics have dense structure and excellent dielectric properties。The best properties of Mg(Ti_0.95Sn_0.05)O₃ ceramics sintered at 1275°C are:ε_r=18.0,Q×f=135500 GHz,τ_f=-60.43 ppm/°C.The(Mg_0.95Zn_0.05)(Ti_0.95Sn_0.05)O₃ ceramics sintered at1275°C have the best properties:ε_r=18.4,Q×f=140400 GHz,τ_f=-64.71 ppm/°C.2.On the basis of the above experiments,I chose Li F as sintering agent andstudy the effect of 4 wt%Li F on Mg(Ti_0.95Sn_0.05)O₃,(Mg_0.95Ni_0.05)(Ti_0.95Sn_0.05)O₃,(Mg_0.95Zn_0.05)(Ti_0.95Sn_0.05)O₃ ceramics.The results show that the addition of 4 wt%Li F as sintering agent can form liquid phase in the sintering process,and can effectively reduce the sintering temperature to 975°C.Mg(Ti_0.95Sn_0.05)O₃-4 wt%Li Fceramics have the best performance at 975°C:ε_r=15.5,Q×f=34900 GHz;The optimum performance of(Mg_0.95Zn_0.05)(Ti_0.95Sn_0.05)O₃-4wt%Li F ceramics at 975°C:ε_r=15.8,Q×f=32804 GHz.3.Taking Mg₂Ti O₄ as the research object,Mg₂Ti O₄-x wt%LCB（x=3.0,4.5,6.0,7.5,9.0,10.0）ceramics were prepared by adding Li F-2Ca F₂-2B₂O₃（LCB）composite sintering agent,and studied the change of sintering properties and microwave dielectric properties of Mg₂Ti O₄ ceramics when x increases from 3.0 to 10.0.XRD results show that the sintered sample is Mg₂Ti O₄ and Ca Ti O₃ two-phase structure,accompanied by a small amount of Mg₃B₂O₆ hybrid phase.SEM results show that the sample sintered at1175°C compact structure.With the increase of x,the bulk density and Q×f value decrease gradually,and theτ_f value increases from-29.6 ppm/C to+16.1 ppm/C.By adjusting x appropriately,the frequency and temperature stable Mg₂Ti O₄-7.5 wt%LCB ceramics can be obtained at 1175°C.The dielectric property of the Mg₂Ti O₄-7.5 wt%LCB ceramics are:ε_r=15.3,Q×f=32950 GHz,τ_f=+1.96 ppm/°CFigure 15;table 13;reference 87...