Research On The Preparation And Dielectric Properties Of SrCuSi₄O₁₀-based Microwave Dielectric Ceramics With Low Permittivity

With the rapid development of mobile communication and satellite communication,microwave dielectric ceramics with low permittivity are required to be developed for high frequency wireless communication technology.And,the microwave dielectric materials used in LTCC field must have a low tan?value,a near zero temperature coefficient,a low sintering temperature.However,the two main problems of ceramics with low dielectric constant as follows:high sintering temperature and bad temperature stability.Therefore,development of low dielectric constant ceramics with low sintering temperature,low loss and a near zero temperature coefficient is the urgent problem to solve at present.SrCuSi₄O₁₀-based ceramics are promising for high frequency wireless communication technology due to their low dielectric constant??_r?and low dielectric loss?tan??.In this thesis,the SrCuSi₄O₁₀ ceramics were prepared by the conventional solid-state method.The effects of preparation processes,sintering aids,TiO₂ and ion substitution on the phase compositions,microstructures and dielectric properties of the ceramics were systematically investigated by XRD,SEM,LCR meter etc.Therefore,the main works of this thesis are summarized as follows:At first,the preparation process of SrCuSi₄O₁₀ ceramics was investigated.The effects of main preparation process parameters on the microstructures,phase compositions and dielectric properties of SrCuSi₄O₁₀ ceramics were investigated.And,the single-phase SrCuSi₄O₁₀ ceramic with a dense microstructure and high bulk density was obtained when it was calcined at 975?,secondary ball milled for 6h and sintered at 1100?.In order to meet the requirement about the LTCC application,Bi₂O₃?LiF and BaCu?B₂O₅?were added into SrCuSi₄O₁₀ ceramics as sintering aids and lowered its sintering temperature.The sintering characterization,microstructures,phase compositions and dielectric properties of the ceramics were investigated systematically.Based on the experimental results,it indicated that Bi₂O₃?LiF and BaCu?B₂O₅?were suitable for SrCuSi₄O₁₀ ceramics as sintering aids.Furthermor,SrCuSi₄O₁₀-3.0wt%Bi₂O₃ ceramics exhibited excellent dielectric properties(?_r=6.26,tan?=3.1×10^-3,??=122.90 ppm/?)sintered at 950?;SrCuSi₄O₁₀-1.0wt%LiF ceramics exhibited good dielectric properties(?_r=5.88,tan?=1.6×10^-3,??=119.90 ppm/?)sintered at 900? and SrCuSi₄O₁₀-8.0wt%BaCu?B₂O₅?ceramics with high performance(?_r=6.09,tan?=1.4×10^-3,??=110.1 ppm/?)sintered at 925?.The TiO₂ with a large negative??value was chosen in order to tailor the large positive??value of SrCuSi₄O₁₀ ceramics.The results showed that,TiO₂ can effectively adjust the SrCuSi₄O₁₀-based ceramics temperature coefficient of dielectric constant.What's more,the SrCuSi₄O₁₀ ceramics with 20.0wt%TiO₂ addition sintered at 1000? for 6h showed excellent dielectric properties:?_r=9.63,tan?=1.8×10^-3 and?_?value of16.7 ppm/?.Addition of 21.0wt%TiO₂ effectively improved the temperature stability of SrCuSi₄O₁₀-1.0wt%LiF ceramics and adjusted the??value?1.80 ppm/??to close to zero sintered at 900? for 6h.Finally,the effects of Ba²⁺and Ca²⁺substitution on the lattice structure and dielectric properties of SrCuSi₄O₁₀ ceramics were investigated.The cell volume increased with the increase of x,when the substitution of Ba²⁺for Sr²⁺.And,the cell volume decreased with the increase of x,when the substitution of Ca²⁺for Sr²⁺.In addition,the influences of ionic substitution on the sintering temperature,bulk density and temperature coefficient of dielectric constant were so little.Moreover,Ba_0.04Sr_0.96CuSi₄O₁₀ ceramic sintered at 1100? showed excellent dielectric properties:?_r=5.97,tan?=1.2×10^-3,??=119.4 ppm/?.Ca_0.06Sr_0.96CuSi₄O₁₀ ceramics exhibited high performance(?_r=6.14,tan?=1.1×10^-3,??=114.6 ppm/?)sintered at 1100?.