| In recent years,with the iterative upgrade and rapid development of communication technology,microwave dielectric ceramic materials have been widely used in 5G communication systems.Generally speaking,we use relative permittivityεr,quality factor Q×f and resonant frequency temperature coefficientτf to evaluate the microwave dielectric properties of microwave ceramics.They are closely related to the application field,loss and temperature stability of microwave materials.Cordierite-type microwave dielectric ceramics(Mg2Al4Si5O18)have the performance characteristics of low dielectric constant,so they can be used in low-latency scenarios.Cordierite microwave ceramics have the problems of narrow sintering temperature range,low quality factor,large negative resonant frequency temperature coefficientτf,high densification sintering temperature,etc.To solve these problems,this article adopts ion substitution and two-phase composite methods to control its microwave dielectric properties,and systematically analyzed the influence of cordierite-type microwave dielectric ceramics’sintering characteristics,phase composition,microscopic morphology,microwave dielectric properties of ceramics,and then using the theoretical knowledge of complex chemical bonds,from the aspects of the ionic property of chemical bonds,lattice vibration energy of chemical bonds,bond energy of chemical bonds and coefficient of thermal expansion of chemical bonds,characterize the internal laws between the important parameters of the chemical bond of Mg2Al4Si5O18 and the microwave dielectric properties of ceramics.The specific research content is as follows:（1）Mg2Al4-2x(Mn0.5Zn0.5)2xSi5O18（0≤x≤0.3）single-phase solid solution ceramics can be obtained by replacing Al3+with Zn2+/Mn4+,and its quality factor has been significantly improved.With the increase of Zn2+/Mn4+content,the dielectric constant fluctuates between 4.4 and 4.8.The quality factor of cordierite ceramics first increases and then decreases with the increase of doping concentration.The temperature coefficient of resonance frequency is-25ppm/℃to-38ppm/℃,the sintering temperature is between 1250℃and 1450℃.When the sintering temperature is1350℃,Mg2Al3.7(Mn0.5Zn0.5)0.3Si5O18 has excellent microwave dielectric properties:εr=4.4,Q×f=150505GHz（at14.541GHz）,τf=-31ppm/℃.（2）Preparation and performance analysis ofTiO2 composite stabilized Mg2Al3.7(Mn0.5Zn0.5)0.3Si5O18 based ceramics.On the basis of the high Q value Mg2Al3.7(Mn0.5Zn0.5)0.3Si5O18,the positive frequency temperature coefficient additiveTiO2（εr=105,Q×f=46000GHz,τf=+465ppm/℃）with higher quality factor is used.Prepare Mg2Al3.7(Mn0.5Zn0.5)0.3Si5O18-xTiO2（x=0,1.6,3.3,5.0,6.8,8.7,10.6wt%）。When 1.6wt%≤x≤10.6wt%,the ceramic presents a composite phase of Mg2Al4Si5O18/TiO2.Composite ceramics obtain near-zero frequency temperature coefficient@1225℃:εr=5.68,Q×f=58043GHz@14.078GHz,τf=-3.11 ppm/℃（x=8.7wt%）,εr=5.82,Q×f=47026GHz@14.128GHz,τf=+2.43 ppm/℃（x=10.6wt%）.（3）Preparation and performance analysis of SrTiO3/CaTiO3 composite Mg2Al3.7（Mn0.5Zn0.5）0.3Si5O18 based ceramics.（1-x）Mg2Al3.7（Mn0.5Zn0.5）0.3Si5O18-x SrTiO3/CaTiO3（x=0,1,2,3,4,5wt%）was prepared by traditional solid-phase process.In this experiment,When 1wt%≤x≤3wt%,cordierite solid solution appeared.When 4wt%≤x≤5wt%,Sr Al2Si2O8/Ca Al2Si2O8 feldspar appeared.As the content of SrTiO3/CaTiO3 increased,the dielectric constant gradually increased and Q×f decreased.95wt%Mg2Al3.7(Mn0.5Zn0.5)0.3Si5O18-5wt%SrTiO3composite ceramics get the best temperature coefficient of resonance frequency when the sintering temperature@1275℃:εr=5.86,Q×f=28023GHz@14.419GHz,τf=-12ppm/℃.95wt%Mg2Al3.7(Mn0.5Zn0.5)0.3Si5O18-5wt%CaTiO3 composite ceramics get the best temperature coefficient of resonance frequency at sintering temperature@1275℃:εr=5.65,Q×f=36033GHz@14.288GHz,τf=-19ppm/℃. |
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