Preparation And Investigation Of Cordierite Based Microwave Dielectric Ceramics

With the gradual development of microwave communications in the direction of high frequency,it is particularly important to ensure the performance and integration of devices at high frequencies.The microwave dielectric ceramics are required to have higher working stability and lower dielectric loss.Cordierite(Mg₂Al₄Si₅O₁₈)microwave dielectric ceramics have low cost and excellent microwave dielectric properties,so they have good application prospects.In this paper,Mg₂Al₄Si₅O₁₈ ceramics are prepared by solid-phase method,and the effects of preparation technology and doping modification on the microstructure and microwave dielectric properties of the materials are discussed.The control variable method was used to explore the preparation process of Mg₂Al₄Si₅O₁₈ ceramics.The effects of pre-firing temperature and sintering temperature on ceramic microstructure and microwave properties,as well as the effects of other processes on ceramic quality factor were studied.By improving the preparation process of Mg₂Al₄Si₅O₁₈ ceramics,the microwave dielectric performance was improved to a certain extent:Q×f=52314 GHz,?_r=4.86,?_f=-28 ppm/?.The inhibitory effect of MgO content on the second phase of Al₆Si₂O₁₃ was investigated.By increasing the content of MgO,the appearance of the second phase of Al₆Si₂O₁₃ was effectively suppressed,and single-phase cordierite ceramic was obtained.the microstructure of the ceramic and the uniformity of the crystal grains were improved by adding MgO.The microwave dielectric characteristics were significantly improved in the nonstoichiometric Mg_2+x+x Al₄Si₅O_18+x ceramics on eliminating the Al₆Si₂O₁₃ secondary phase,where enhanced the quality factor.The best microwave dielectric performance was obtained at an excess of 0.2mol of MgO:?_r=5.18,Q×f=86374GHz,?_f=-27 ppm/?The temperature coefficient of resonance frequency of Mg_2.2Al₄Si₅O_18.2 was adjusted by adding TiO₂.The experimental results showed that the density of Mg_2.2Al₄Si₅O_18.2 ceramics was increased by forming a solid solution with TiO₂,and he temperature coefficient of resonance frequency of Mg_2.2Al₄Si₅O_18.2 ceramics was adjusted by he precipitated rutile phase.When the content of TiO₂ was 6wt%,the ceramic obtained high quality factor and high temperature stability.Its microwave dielectric properties were Q×f=68264 GHz,?_r=5.56,?_f=-9.95 ppm/?.When the content of TiO₂ was 8wt%,the ceramic obtained a near-zero temperature coefficient of resonance frequency?_f=-3.62ppm/?,Q×f=56626 GHz,and?_r=5.84.The influence of RO₂?R=Ce,Mn,Zr,Sn?on the microstructure and the microwave dielectric properties of Mg₂Al₄Si₅O₁₈ ceramic materials was investigated.The experimental results showed that the density of ceramics were increased by orming a solid solution.The quality factor and growth of ceramic grains were improved by adding MnO₂.The temperature coefficient of the resonance frequency was adjusted by adding ZrO₂.With CeO₂ doping,?-cordierite was converted into?-cordierite,which led to a decrease in the ceramic quality factor.The sintering temperature was reduced and the sintering interval was widend by adding SnO₂.In the range of 60?,the fluctuation of the quality factor of Mg₂Al₄Si₅O₁₈-SnO₂ ceramics was less than 5000 GHz.