Research On Low-permittivity Microwave Dielectric Ceramics

As key materials of modern communication technology,microwave dielectric ceramics have aroused extensive attention all over the world.With the expansion of wireless communication frequency bands to millimeter-wave,the development of low-permittivity microwave dielectric ceramics with high performance has become a research hotspot.In this paper,the modification of low-permittivity silicate CaMgSi2O6 ceramics was investigated,and the regulation mechanism of ion substitution on microwave dielectric properties was explored.In addition,BaZnP2O7 and SrZnV2O7 low-permittivity microwave dielectric ceramics with intrinsic low sintering temperatures have been developed in order to meet the application requirements of low-permittivity systems in the field of LTCC(Low Temperature Co-fired Ceramic).Based on the feasibility analysis of ion substitution,Ca1-xSrxMgSi2O6 and CaMg1-xMnxSi2O6 ceramics were prepared by the substitution at A site and B site,respectively.The improved microwave dielectric properties with εr=8.17,Q×f=85858 GHz,τf=-41.25 ppm/℃(Ca0.96Sr0.04MgSi2O6)and εr=8.01,Q×f=83469 GHz,τf=-45.27 ppm/℃(CaMg0.98Mn0.02Si2O6)were obtained,and the internal mechanism of dielectric properties controlled by ion substitution was systematically studied.The effects of Raman shift and the full width at half maximum of Raman scattering peaks on the dielectric constant and dielectric loss of Ca1-xSrxMgSi2O6 ceramics were researched by Raman spectroscopy.The infrared reflection spectrum of the CaMg0.98Mn0.02Si2O6 ceramic was fitted by the classical resonator model,and the minimum of dielectric loss was calculated,which provided a theoretical reference for the development of CaMgSi2O6-based ceramics.Adding low melting point oxides,adopting wet chemical methods or new sintering methods to reduce sintering temperatures of ceramics usually deteriorate dielectric properties or increase the cost.Therefore,B aZnP2O7 ceramics with intrinsic low sintering temperatures were prepared in this paper,which possessed excellent dielectric properties:εr=8.23,Q×f=56170 GHz and τf=-28.7 ppm/℃.The dielectric constant and dielectric loss of BaZnP2O7 ceramics depended on the relative density of ceramics.τf values fluctuated around-28 ppm/℃,showing a weak dependence on the sintering temperature.Mg2+ was used to substitute for Zn2+to form BaZn1-xMgxP2O7 infinite solid solution,which improved microwave dielectric properties of BaZnP2O7 ceramics.The complex chemical bond theory was used to calculate the dielectric susceptibility,lattice energy and bond energy of BaZn1-xMgxP2O7 crystal,and the change of microwave dielectric properties was explained from the perspective of structure-property.The BaZn0.98Mg0.02P2O7 ceramic sintered at 900℃ exhibited excellent microwave dielectric properties(εr=8.21,Qxf=84760 GHz and τf=-21.9 ppm/℃)and chemical compatibility with Ag electrode,possessing the potential for LTCC technology.The temperature range of SrZnV2O7 phase forming and the suitable calcination temperature were determined by TG-DSC(Thermo Gravimetric-Differential Scanning Calorimetry).Combined with TG-DSC and XRD(X-ray Diffraction),it was confirmed that chemical reaction began at 420℃,namely,phase SrZnV2O7 was formed by SrCO3 and ZnV2O6,and the calcination temperature of SrZnV2O7 ceramics was in the range of 610～700℃.XRD and TEM(Transmission Electron Microscope)analysis showed that SrZnV2O7 crystallized in monoclinic structure with P21/n space group.Raman spectroscopy was used to study the vibration characteristics of SrZnV2O7 crystal.The samples sintered in the atmosphere of air,oxygen and nitrogen were separately tested by XPS(X-ray Photoelectron Spectroscopy).It was found that the reduction of V5+to V4+existed in all samples.Electrochemical impedance spectroscopy and XPS confirmed that oxygen vacancies were generated during the sintering process of SrZnV2O7 ceramics,which led to the reduction of V5+ and then the deterioration of Qxf value.The SrZnV2O7 ceramic possessed an intrinsic low sintering temperature(740℃),excellent dielectric properties(εr=11.28,Q×f=56660 GHz and τf=-27.2 ppm/℃)and chemical compatibility with Ag electrode,which made it a candidate material in the field of LTCC.A dielectric resonator antenna was designed using HFSS simulation software and then was fabricated,realizing the device verification of SrZnV2O7 ceramics.