Study On The Preparation And Microwave Dielectric Properties Of Li₂O-TiO₂-MgO Ceramics

Microwave dielectric ceramic is one of the indispensable materials in mobile communication technology.Li₂O-TiO₂-MgO?LTM?ceramics are the important components of the microwave dielectric ceramics.LTM ceramics have excellent microwave dielectric properties,but high sintering temperature,narrow range of sintering or unsuitable permittivity restricted their applications in microwave components.In this paper,a series of LTM microwave dielectric ceramics with good properties were obtained by changing composition,adding sintering aid,pretreating the raw material.Besides,the microwave dielectric properties of 2Li₂O-AO-3WO₃?A=Mg,Zn?ceramics were also studied.The main contents were as follows:?1?Specimens of Mg_1-xLi_2xTi_xO_1+2x?1/5?x?1/2?solid solution ceramics were synthesized via the conventional solid state reaction method.The sintering characteristics,microstructure and microwave dielectric properties of ceramics were studied.XRD dates presented that Li₂TiO₃ and MgO could form Mg_1-xLi_2xTi_xO_1+2x+2x solid solutions with a rock salt structure.The unit cell parameters of Mg_1-xLi_2xTi_xO_1+2x+2x solid solutions decreased with increasing x values.The Q×f value and bulk density improved firstly and then deteriorated as the content of Li₂TiO₃ increased.Li₂Mg₃TiO₆ ceramics shown good microwave dielectric properties with Q×f of110,703 GHz,?_r of 13.6 and?_f of-35.1 ppm/^oC.?2?Li₂O-3MgO-mTiO₂?1?m?6?systems were produced by the traditional solid state reaction method.The phase composition and microstructure of ceramics were studied by the X-ray powders diffraction,scanning electron microscopy and energy dispersive spectrometer techniques.With increasing the content of TiO₂ addition,the optimized sintering temperature of Li₂O-3MgO-mTiO₂ ceramics decreased from 1275^oC to 1050 ^oC.The good microwave dielectric properties of Li₂O-3MgO-5TiO₂ceramics sintered at 1050 ^oC with Q×f about 71,726 GHz,?_r about 21.9 and?_f about-20.9 ppm/^oC were obtained.?3?The effects of BaCu?B₂O₅??BCB?addition on the sintering temperature and microwave dielectric properties of Li_4/5Mg_4/5Ti_7/5O₄?LMT?ceramics were studied.The best microwave dielectric properties of 0.97LMT-0.03BCB ceramics sintered at900 ^oC with?_r=20.9,Q×f=42,104 GHz and?_f=-24.0 ppm/°C were obtained.TiO₂was used to improve the?_f value of 0.97LMT-0.03BCB.The good microwave dielectric properties of 0.85?0.97LMT-0.03BCB?-0.15TiO₂ ceramics sintered at 875^oC with?_r=23.1,Q×f=37,700 GHz and?_f=-5.9 ppm/°C were got.Importantly,0.85?0.97LMT-0.03BCB?-0.15TiO₂ ceramics have a good compatibility with Ag.?4?Li₂MgTiO₄ ceramics were prepared using the milled high-purity powders and untreated high-purity powders as the raw materials,respectively.Li₂MgTiO₄ ceramics prepared by the milled high-purity powders shown good microwave dielectric properties with moderate?_r?15.8¹6.2?,high Q×f value?80,805⁹0,902 GHz?and negative?_f value?-30^-24.5 ppm/^oC?at a wide range of sintering temperature?1125¹275 ^oC?.By contrast,Li₂MgTiO₄ ceramics prepared by the untreated high-purity powders presented the good microwave dielectric properties only at a narrow range of sintering temperature.?5?The phase compositions and microwave dielectric properties of2Li₂O-AO-3WO₃?A=Mg,Zn?low-firing microwave dielectric ceramics were studied.The bulk density,Q×f and?_r increased firstly and then decreased with increasing the sintering temperature.The good microwave dielectric properties of2Li₂O-MgO-3WO₃ and 2Li₂O-ZnO-3WO₃ ceramics were obtained at 700 ^oC and 675^oC,respectively.Besides,2Li₂O-AO-3WO₃?A=Mg,Zn?ceramics have a good chemical compatibility with Ag,which imply that they can act as a commercial LTCC materials.