Sol-gel Preparation Of Li₄Mg₃Ti₂O₉ Nanopowders And Low-temperature Sintering And Microwave Of Ceramics Dielectric Performance Regulation

Microwave dielectric ceramics are developed in recent 20 years.Due to the suitable dielectric constant,low dielectric loss and thermal stability,they are widely concerned.Microwave dielectric materials can be made into dielectric resonator,waveguide transmission,and the microwave dielectric antenna and so on,which can complete the transmission,reflection,absorption of electromagnetic waves and achieve the microwave modulation.It is reported that Li₄Mg₃Ti₂O₉ ceramics have advantage of excellent microwave properties except that sintering temperatures about 1450 ? is too high.On the one hand,the evaporation of Li element at high temperature degradates the microwave dielectric properties;on the other hand,high sintering temperature impedes application in the LTCC technology.In this paper,Li₄Mg₃Ti₂O₉ nanopowders were fabricated through a sol-gel method.Li₄Mg₃Ti₂O₉ nanopowders with addition of LiF were used to lower the sintering temperature.?1-x?Li₄Mg₃Ti₂O₉-xCaTiO₃?0<x ? 0.2?added with 4wt%LiF was prepared to adjust the microwave dielectric properties.The main research rusults are as follows:?1?The influences of preparation conditions on the phase components and micro structure of Li₄Mg₃Ti₂O₉ nanopowders were investigated.Li₄Mg₃Ti₂O₉nanopowders with the average particle size of 37 nm,good dispersion and high activity were fabricated by a sol-gel method,and then the powders were used as raw material to prepare the Li₄Mg₃Ti₂O₉ based ceramics.At 1275 ?,the Li₄Mg₃Ti₂O₉ ceramics showed good microwave dielectric properties of ?f=15.5,Q×f= 85300 GHz and ?f ?-31 ppm/?.?2?The addition of LiF was used to further reduce the sintering temperature of Li₄Mg₃Ti₂O₉ ceramics.The sintering temperature of Li₄Mg₃Ti₂O₉ ceramics was decreased from 1275 ? to 850?1000 ? after addition of LiF.Meanwhile,microwave dielectric properties were not degradated.On the one hand,the substitution of F-ion for O2-in Li₄Mg₃Ti₂O₉ compound promoted the sintering process;On the other hand,the formation of LiF-MgF2 liquid phase reduced the sintering temperature.The Li₄Mg₃Ti₂O₉-4wt%LiF ceramics sintered at 850 ? showed great microwave dielectric properties of ?r=17.5,Q×f= 89320 GHz and ?f=-37.4 ppm/?.Considering the wide sintering temperature window?850?1000 ??and good compatibilility with Ag electrodes,the present material was promising to be a potential candidate for LTCC application.?3?Li₄Mg₃Ti₂O₉ and CaTiO₃ nanopowders were prepared via a sol-gel method.?1-x?Li₄Mg₃Ti₂O₉-xCaTiO₃?0<x<0.2?composite ceramics were prepared to adjust the temperature coefficient of resonant frequency??f?.LiF was used as sintering agent to reduce the sintering temperature.At temperature range of 750?950 ?,all samples had well,densified microstructures and temperature-stable microwave dielectric properties.The average grain size of samples had no obviouse change with increasing CaTiO₃ content x.The ?r gradually increased from 17.9 to 20.1 and temperature coefficient of resonant frequency increased from-33.8 ppm/? to +8 ppm/? as x increased,while the Q×f value decreased from 32840 GHz to 21740 GHz Excellent microwave dielectric properties with ?r= 19.5,Q×f = 25790 GHz and ?f=-5.8 ppm/? were obtained for x =0.5 composition sintered at 850 0C.In addition,the influence of LiF content on phase component,microstructure,sintering behavor and microwave dielectric properties of Li4Mg3TizO9-CaTiO₃ composite ceramics were investigated.The densification temperature of Li₄Mg₃Ti₂O₉-CaTiO₃ composite ceramics was further reduced to 750 ? due to the substitution of F-ion for O^2-and Li⁺ for Mg²⁺ in Li4Mg3Ti2o coMpound,nanopowders and formation of LiF-CaF₂ liquid phase.The Li₄Mg₃Ti₂O₉-CaTiO₃ composite ceramics with addition of 7wt%LiF showed great microwave dielectric properties??r=18.2,Q×f= 82100 GHz?.