Study On Phase Compositions,Structures And Dielectric Properties Of The SrO-CeO₂ Series Microwave Ceramics Used In Wave Filters

Due to its unique crystal structure type,ABO₃ type perovskite microwave ceramics can be used to regulate the dielectric properties of matrix materials through ion doping,solid solution,or composite with other phase structure ceramics.Therefore,scholars in this field have received extensive attention.Currently,research on SrCeO₃ perovskite ceramics mainly focuses on optical and electrothermal aspects,and exhibits excellent physical and chemical properties as well as luminescent properties.This indicates that this system has potential research value in ABO₃ type functional ceramic materials,but there are few systematic reports on its microwave dielectric properties.Based on this,this article selects SrCeO₃ as the matrix material,and comprehensively analyzes the phase composition,structure,and dielectric properties of SrO-CeO₂series microwave ceramic materials by doping Ti⁴⁺-,Zr⁴⁺-ions,and composite Sr₂CeO₄ceramics,with the aim of regulating and optimizing the microwave dielectric properties of the system（mediumε_r.Higher Q×f value and near-zeroτ_fvalue）.At the same time,the dielectric performance parameters of the optimal component ceramic system are used for the simulation design of dielectric substrate microstrip line filters,providing support for the development of alternative substrate materials for 5G communication filters.The main research content and results are as follows:（1）Zr⁴⁺-and Ti⁴⁺-ions doped SrCeO₃ based microwave ceramic systems(SrCe_1-xTi_xO₃ and SrCe_1-xZr_xO₃ ,x=0-0.1)were prepared by a solid-state reaction method.The correlation between the phase structure,microstructure,and microwave dielectric properties of each system was studied in detail:The XRD results show that with the increase of the doping content of Ti⁴⁺-and Zr⁴⁺-ions,SrCe_1-xTi_xO₃ and SrCe_1-xZr_xO₃ ceramics can basically form solid solution,which belongs to an orthogonal perovskite structure with a space group of Pmcn（62）;At the same time,it was observed through SEM images that the grain size of samples with different components is relatively uniform,with high density and very little impurity content.Combined with the test results of SEM-EDS on the distribution and content of various elements,the correctness of XRD pattern analysis can also be verified.In addition,by analyzing the fitting results of complex plane impedance spectroscopy,it can be seen that the temperature stability of Ti⁴⁺-ions doped SrCeO₃ solid solution ceramics is better than that of Zr⁴⁺-ions doped systems,wherein SrCe_1-xTi_xO₃ （x=0.03）ceramics sintered at 1270°C for 4h can obtain near-zeroτ_fvalue（0.08 ppm/°C）,at this timeε_r=50.2 and Q×f=8,940 GHz（f₀=5.91 GHz）.（2）To further enhance the quality of SrCeO₃ matrix Q×f value is compounded with perovskite like Sr₂CeO₄ceramics with low dielectric loss and belonging to the same orthogonal structure.The ceramic system is prepared by using a solid-state reaction method according to the chemical formula（n+1）SrO-n CeO₂（n=2）.The XRD analysis results show that the system is a composite ceramic system（represented as SrCeO₃ +Sr₂CeO₄）with coexistence of SrCeO₃ and Sr₂CeO₄phases,which belongs to the orthogonal Pmcn（62）and Pbam（55）space group respectively.On this basis,the relationship between the phase composition,microstructure morphology,and microwave dielectric properties of this composite system doped with different Ti⁴⁺-ions was explored through characterization methods such as Raman spectroscopy,SEM-EDS,and HRTEM（SAED）.The x TiO₂-（1-x）（SrCeO₃ +Sr₂CeO₄）composite system sintered at 1330℃for 4 h at x=0.2 has microwave dielectric properties suitable for filter substrate materials:mediumε_r=40.3,higher Q×f=4,4020 GHz（f₀=6.56 GHz）and in the practical rangeτ_f=-4.6 ppm℃.（3）Based on the microwave dielectric properties of the superior Ti⁴⁺-ions regulated composite system mentioned above,a parallel coupled microstrip line filter with a center frequency of 6.56 GHz was simulated and designed.By setting the parameters of in band return loss,insertion loss,and passband bandwidth involved in the modeling,and combining the simulation analysis results such as S-parameter curves,the microstrip line filter structure was improved.The simulation results after structural optimization showed that the filter has good physical and chemical properties and strong anti-interference ability,indicating the feasibility of Ti⁴⁺-ions modified SrCeO₃ +Sr₂CeO₄ceramic composite system as a matrix material for filters in microwave circuits with better components.