Structure,Microwave Properties And Low Temperature Co-firing Of （Zn,Mg）_2-xSiO_4-x-Based Microwave Ceramics

Zn₂SiO₄-based microwave ceramics with low dielectric constant and low dielectric loss have broad application prospects in chip ceramic filters.However,the crystal structure of Zn₂SiO₄-based ceramics is complex.The symmetry of the crystal structure with equilateral hexagonal rings composed of Zn（1）O₄,Zn（2）O₄ and SiO₄ tetrahedra as well as the average oxygen tetrahedral distortion in the Zn₂SiO₄ crystal has a significant impact on the microwave properties.This paper attempts to clarify the relationship between the structure and properties of Zn₂SiO₄-based ceramics through the effects of Zn deficiency and Mg doping on Zn₂SiO₄-based ceramics under non-stoichiometric ratios.In addition,the sintering temperature of Zn₂SiO₄-based ceramics is as high as 1300°C,which does not meet the requirements of Low Temperature Cofired-Ceramics（LTCC）.Therefore,this paper reduces the sintering temperature by adding Ba Cu（B₂O₅）as a sintering aid,and explores the effect of the addition of sintering aid on structure and microwave properties of Zn₂SiO₄-based ceramics.The research results of this paper are as follows:（1）With the increase of Zn deficiency in Zn_2-xSiO_4-x（x=0,0.1,0.2,0.3,0.4）ceramics,the volume of the unit cell gradually decreases,and symmetry of the crystal structure is enhanced.As x increases,the theoretical molecular polarizability decreases,resulting in a decrease in theε_r of ceramics from 6.7 to 6.3.Theτ_fincreases linearly with the oxygen tetrahedral distortion.In the range of x=0.1～0.2,higher symmetry of the crystal structure with equilateral hexagonal rings leads to higher Q×f values.The Zn/Si ratio further deviates from the stoichiometric ratio as x further increases leads to increase of the liquid phase content and decrease of the grain size,resulting in a decrease in the Q×f values.At x=0.2,the Zn_1.8SiO_3.8 ceramics sintered at 1300°C indicate excellent dielectric properties:Q×f=83,500 GHz,ε_r=6.4,τ_f=-21.8×10^-6/°C.（2）The Zn₂SiO₄ main phase with willemite structure was formed in Mg_xZn_1.8-xSiO_3.8（x=0.1,0.2,0.3,0.4）ceramics based on Zn_1.8SiO_3.8.With the increase of Mg doping amount,the volume of the unit cell gradually decreases,the average oxygen tetrahedral distortion increases,and the symmetry of the crystal structure is enhanced,while the bond length of the Zn（Mg）-O bond is reduced.As x increases,the theoretical molecular polarizability decreases,resulting in a decrease in theε_r.Theτ_fincreases with the increase of oxygen tetrahedral distortion.In the range of x=0.1～0.4,higher symmetry of the crystal structure with equilateral hexagonal rings and higher energy of the Zn（Mg）-O bond leads to an increase of Q×f value from 90,500 GHz to 112,100 GHz.At x=0.4,the Mg_0.4Zn_1.4SiO_3.8ceramics sintered at 1300°C indicate excellent microwave properties:Q×f=112,100 GHz,ε_r=6.2,τ_f=-19.2×10^-6/°C.（3）The sintering temperature of ceramics based on Mg_0.4Zn_1.4SiO_3.8can be reduced from 1300℃to 925℃by adding Ba Cu（B₂O₅）as sintering aids.Theε_r changes of Mg_0.4Zn_1.4SiO_3.8-x wt.%Ba Cu（B₂O₅）（x=2,5,8,10）ceramics were caused by density changes when sintered at 925℃,and theτ_f increases with the addition of sintering aids.When the addition content of Ba Cu（B₂O₅）is 2～5 wt.%,the density of the sample increases,so that the Q×f value of the sample increases,However,with the further increase of Ba Cu（B₂O₅）addition,the content of the second phase increases significantly,resulting in the decrease of the Q×f value.Mg_0.4Zn_1.4SiO_3.8-2wt.%ceramics sintered at 925℃for 4 h indicate a good combination of microwave dielectric characteristics:ε_r=6.4,Q×f=20,200GHz,τ_f=-21.4×10^-6/°CThis thesis consists of 46 figures,8 tables,103 references...