Study On Preparation And Properties Of Garnet-type Microwave Ceramics

In this information age of cloud technology,the Internet of Things,and 5G communications,People urgently hope that microwave communication systems can improve signal transmission speed,quality and miniaturization.As an important basic material for microwave communication systems,microwave dielectric ceramic materials are widely used in various fields.In recent years,garnet structure microwave ceramics(A3B2C3O12)have become the research target of researchers due to their low dielectric constant(εr)and high quality factor(Q ×f),However,its ultra-high sintering temperature and large negative resonant frequency temperature coefficient(τf)limit its production and application.In this paper,the high-temperature solid-phase reaction method is mainly used to prepare Y3Al5O12 garnet structure and its modified ceramics.The specific research is as follows:(1)Prepare Y3Mg1-xMnxAl3SiO12(x=0-0.2)ceramics using high temperature solid phase method.XRD and SEM analysis show that when a small amount of Mn2+ions(x<0.1)is incorporated,the ceramic is a single phase,otherwise a Y4.6(SiO4)3O phase will be produced.The volume density,ion polarizability,and second phase of the ceramic jointly determine its relative permittivity.As the value of doping concentration x increases,the packing fraction and relative density of ceramics also increase,and the Q×f value increases.When x=0.2,a large amount of Mn2+ undergoes electronic transitions,which causes the dielectric loss of the ceramic to increase,and the Qxf value decreases.The bond price of Mg/Mn-0 determines the value of τf,and the two show similar trends.Y3Mg2.9Mn0.1Al3SiO12 ceramics have the best microwave dielectric properties when the sintering temperature is 1575℃:εr=10.64,Q×f=62824 GHz,τf=-34.8ppm/℃.(2)Prepare Y3MgxAl5-2xSixO12(x=0-2)ceramics by high temperature solid phase method.XRD and SEM analysis show that the diffraction peaks of all doped samples are matched with Y3Al5O12.When x=2,there is a slight diffraction peak of MgY4Si3O13 in the ceramic.The incorporation of Mg2+/Si4+ions reduce the sintering temperature and time of densified ceramics.The relative permittivity of ceramics is related to the density and ion polarizability of ceramics.The effect of Mg2+/Si4+doping on the Qxf value of ceramics was studied by calculating the packing fraction and grain size of ceramics.τf value has a certain optimization,and its changing trend is closely related to the bond valence of Mg/Al-O and Al/Si-O.Y3Mg0.5Al4Si0.5O12 ceramics obtain excellent microwave dielectric properties when sintered at 1625℃:εr=10.37,Q×f=67571 GHz,τf=-35.23 ppm/℃.(3)MgxY3-xAl5-xSixO12(x=0,0.1,0.3,0.5,0.6)ceramics were prepared by hightemperature solid-phase method,and the influence of different Mg2+/Si4+ions instead of Y3+/A13+on ceramics was studied.XRD and SEM analysis show that when the doped amount x of Mg2+/Si4+is less than 0.6,the ceramic is single-phase,otherwise the phase of MgAl2O4 appears.The existence of MgO-SiO2 liquid phase reduces the sintering temperature and duration of densified ceramics.Refinement and right shift of XRD diffraction peaks proved that Mg2+entered the Y3+ion site to generate inverse garnettype microwave ceramics,and the rattling effect occurred,which caused the abnormal increase of the dielectric constant of the ceramics.As the value of x increases,the bond value of Mg/Y-0 decreases and the abnormal growth of ceramics increases the dielectric loss of the ceramics,and the Qxf value decreases.In addition,the change of Qxf value is related to the half-width of the Eg peak of the Raman spectrum.The increase of the Mg/Y-0 bond length and the uneven distribution of crystal grains in the ceramic make the τf of the ceramic show a trend of first rising and then falling.Mg0.1Y2.9Al4.9Si0.1O12 shows higher dielectric properties at 1575℃:εr=10.67,Q×f=58799.5 GHz,τf=-29.5 ppm/℃.