Preparation And Microwave Dielectric Properties Of Li₂Mg₃Ti O₆ Based Ceramics

Wireless communication technology is constantly changing.The joint development of 5G network and a variety of new technologies provides great convenience for people’s current life,which is inseparable from basic material research and application.Various communication related devices made of dielectric ceramics have been widely used in various fields,but also face the challenge of higher requirements in the new era.Therefore,as the basic core material,the research,development and application of new microwave dielectric ceramics have attracted more attention.In this paper,Li₂Mg₃TiO₆ ceramic system was selected as the basic material,and Li₂Mg₃Ti_1-x(Al_0.5Nb_0.5)_xO₆ and Li₂(Mg_1-yZn_y)₃Ti_1-x(Al_0.5Nb_0.5)_xO₆ dielectric ceramics were prepared by doping and replacement at Ti and Mg sites by solid-state method.Then,Li₂(Mg_1-yZn_y)₃Ti_1-x(Al_0.5Nb_0.5)_xO₆+Ba Cu B₂O₅ dielectric ceramics were prepared by cooling sintering with sintering additives.According to the amount of doping,this paper studied the above ceramics from the aspects of ceramic density,phase change,crystal structure,bond valence theory,stacking coefficient and sintering kinetics,and obtained some dependence on the dielectric properties of the ceramics.Li₂Mg₃Ti_1-x(Al_0.5Nb_0.5)_xO₆ dielectric ceramics doped and replaced at the Ti site of Li₂Mg₃TiO₆ by solid-state method are a single phase with rock salt cubic structure in the experimental range.Through the analysis of P-V-L chemical bond valence theory and the calculation of various parameters related to bond properties,it is found that(Al_0.5Nb_0.5)⁴⁺ion doping improved the ionic polarizability,increases the lattice energy,increases the chemical bond valence and decreases the thermal expansion coefficient with the increase of doping amount.These changes work together to improve the dielectric properties of Li₂Mg₃TiO₆ceramics,improved the quality factor,dielectric constant,temperature stability,and reduced sintering temperature.The best dielectric properties are obtained when the doping amount of(Al_0.5Nb_0.5)⁴⁺is x=0.09（ε_r=13.86,Q×f=141210 GHz,τ_f=-25.9 ppm/℃）.On this basis,Zn²⁺ion was further doped and replaced at its Mg site by the same solid-state method.When the doping amount is less than 0.08,the ceramic is a single crystalline phase.Excessive doping leads to the formation of heterophases and worsens the dielectric properties.An appropriate amount of Zn²⁺ion doping can further improve the comprehensive dielectric properties and reduce the sintering temperature.When the doping amount of Zn²⁺ion is y=0.08,Li₂(Mg_0.92Zn_0.08)₃Ti_0.91(Al_0.5Nb_0.5)_0.09O₆ ceramics sintered at 1320℃for 4 hours have the comprehensive optimization dielectric properties,ε_r=14.51,Q×f=158120 GHz,τ_f=-13.0 ppm/℃.Based on this,Ba Cu B₂O₅ was added to Li₂(Mg_0.92Zn_0.08)₃Ti_0.91(Al_0.5Nb_0.5)_0.09O₆dielectric ceramics to explore the cooling sintering.The results show that the addition of Ba Cu B₂O₅will introduce impurity phase into the system,and liquid phase will be produced in the ceramics.Although the sintering temperature decreases rapidly with the increase of Ba Cu B₂O₅ content,ooling sintering can be realized,but also with the decrease of quality factor and temperature stability.The best comprehensive properties can be obtained by holding the temperature at 1060℃for 4 hours,ε_r=14.22,Q×f=31054 GHz,τ_f=-15.9ppm/℃.