Dielectric Properties And Phase Structure Of MgO-TiO₂ Microwave Dielectric Ceramics

The introduction of 5G communication technology has contributed to the development of various industries,including microwave communication equipment.Dielectric microwave ceramics plays an important role in the 5G era as a material for the manufacture of essential components for 5G communication devices.Electronic components need to work in a variety of temperature environments all over the world,and the heat generated by working operation leads to a wide range of operating temperature,so good temperature stability is the key to the wide application of microwave dielectric ceramics.At present,there is little research on the stability of microwave dielectric ceramics at a wide temperature range,especially at sub-zero temperature.In this experiment,the phase structure and property optimization of MgO-TiO₂microwave dielectric ceramics were systematically investigated by the conventional solid-phase synthesis process.1、The sintering temperature of the powder lower than the synthesis temperature or higher than the minimum synthesis temperature will have a negative effect on the sintering,microstructure and microwave dielectric properties of the MgTiO₃-Mg₂TiO₄-CaTiO₃（MMC）ceramic.The optimal calcining temperature of MgTiO₃,Mg₂TiO₄ and CaTiO₃ is 1150℃,1250℃and 1100℃,respectively.If the pre-firing temperature is lower than the minimum synthesis temperature,the expected target phase will not be synthesized.If the pre-firing temperature is higher than the minimum synthesis temperature,the activity of the powder will be reduced,and then the sintering microstructure and dense sintering will be affected.If the particle size is too small or too large,it will also have a negative effect on the sintering and microwave dielectric properties of MMC ceramics.If the particle size is too small,the sintered grains will be small and the compactness is poor.If the particle size is too large,the grains will grow abnormally,accompanied by crystal defects,and then deteriorate the dielectric properties.The optimal particle size was 1.88μm in volume fraction D50 and 5.41μm in volume fraction D90.The microwave dielectric properties of MMC ceramics were greatly affected by sintering temperature and holding time.The optimal sintering condition was holding at 1350℃for 6 hours.When the sintering temperature is lower than 1350℃or the holding time is less than 6h,MMC ceramics have poor compactness and smaller grains.When the sintering temperature is higher than 1350℃,MMC ceramics will produce a large number of oxygen vacancy defects,which will lead to poor microwave dielectric properties of MMC ceramics.2、In the range of components studied,Mg₂TiO₄ can improve the densification of MMC ceramics,and the Raman vibration of MMC ceramics is mainly contributed by MgTiO₃.The increase of Mg₂TiO₄ can effectively reduce the half-height width（FWHM）of the vibration of MMC ceramics[TiO₆],so as to improve the Q×f value of MMC ceramics and reduce the dielectric loss.Mg₂TiO₄,MgTiO₃ and CaTiO₃ have synergistic effect on improving the microwave dielectric properties of MMC ceramics.The increase of Mg₂TiO₄ can effectively increase the Q×f value of MMC ceramics,but decrease theε_r value.The increase of MgTiO₃can increase theε_r value of MMC ceramics.Theε_r value of MMC ceramics can be increased rapidly with the increase of CaTiO₃,but the Q×f value will decrease sharply.Mg₂TiO₄,MgTiO₃ and CaTiO₃ have complementary effects on the regulation of the temperature coefficientτ_f of the resonant frequency of MMC ceramics.Mg₂TiO₄ and MgTiO₃ have small negativeτ_f value in the high and low temperature sections,while CaTiO₃ has a larger positiveτ_f value.The phase composition,especially the content of CaTiO₃,has a great influence on theτ_f value of MMC pottery.By changing the phase composition,theτ_f value of MMC can be effectively regulated in a wide temperature range（-40℃～120℃）.The 0.32Mg₂TiO₄-0.611MgTiO₃-0.069CaTiO₃ ceramics have better comprehensive microwave dielectric properties,ε_r=19.7,Q×f=55400GHz,τ_f=-0.34ppm/℃（-40℃～120℃）.3、The optimum sintering condition for MgTiO₃-Mg₂TiO₄-Na_0.5La_0.5TiO₃（MMNL）ceramics is 1440℃for 6h.Too low sintering temperature leads to large porosity and poor sintering densification of MMNL ceramics,and too high sintering temperature leads to abnormal grain growth,with the increase of crystal defects,thus affecting the microwave dielectric properties of MMNL ceramics.The 0.21MgTiO₃-0.653Mg₂TiO₄-0.137Na_0.5La_0.5TiO₃ ceramics have better comprehensive microwave dielectric properties,ε_r=17.5,Q×f=62800GHz,τ_f=-0.35ppm/℃（-40℃～120℃）.Both Na_0.5La_0.5TiO₃ and CaTiO₃ are perovskite crystals and have higher positiveτ_f value.Compared with MgTiO₃-Mg₂TiO₄-CaTiO₃（MMC）ceramics,Na_0.5La_0.5TiO₃ and CaTiO₃ are efficient regulators.MgTiO₃-Mg₂TiO₄-Na_0.5La_0.5TiO₃（MMNL）ceramics have lower loss,higher Q×f value,but relatively smallε_r value.