Study On The Synthesis And Dielectric Characteristics Of Microwave Dielectric Ceramic Material MgNb₂O₆

The rapid development of electronic equipment,power system,vehicle-mounted radar,and 5G communication has put forward more new requirements for electronic components,especially the miniaturization,high-frequency,integration,high performance and multi-function.Low-temperature co-fired ceramics（LTCC）technology has attracted much attention because of its high capacity for miniaturization of electronic systems and hybrid integration.Therefore,the LTCC materials should have a low sintering temperature,a relatively small dielectric constant（ε_r）,a low dielectric loss（i.e.,a high Q×f value）and a near-zero resonant frequency temperature coefficient（τ_f）.However,many LTCC materials could not maintain excellent dielectric properties when sintered at low temperature.In this paper,Columbite-structure MgNb₂O₆ dielectric ceramics were selected and the effect of preparation process and doping modification on the sintering behavior and microwave dielectric properties to satisfy the requirements of LTCC technology.The specific work is as follows:The synthesis process of MgNb₂O₆ ceramics was investigated to discuss the effect of sintering temperature on the microstructure and dielectric properties.Results show that proper pre-sintering temperature can perfectly restrain the formation of second phases.The excellent dielectric properties were obtained for MgNb₂O₆ ceramics when sintered at 1300℃for 5h:ε_r=20.82,Q×f=134000GHz,τ_f=-62.3ppm/℃.Three low melting point materials,namely LMZBS,LBSCA and BaCu（B₂O₅）low melting point materials were chosen to reduce the sintering temperature of MgNb₂O₆dielectric ceramics.And the effects of doping concentration on the phase purity,microstructure,apparent density and microwave dielectric properties of dielectric ceramics were investigated emphatically.The experimental data show that:（1）The LMZBS glass adding could significantly reduce the sintering temperature and achieve high densification of MgNb₂O₆ ceramics with outstanding dielectric properties.The SEM results show dense and homogeneous microstructure with grain size of 1.72 mm.Raman spectra and XRD patterns indicate the pure phase MgNb₂O₆ ceramic.The MgNb₂O₆ceramics doped with 1.0 wt.%of LMZBS glass exhibited remarkable dielectric properties:ε_r=19.7,Q×f=67839GHz,τ_f=-41.01ppm/℃.Moreover,the favorable chemical compatibility of the Mg Nb2O6 ceramic with silver electrodes makes it as promising material for LTCC applications.（2）Doped LBSCA glass can effectively reduce the sintering temperature of dielectric materials,and MgNb₂O₆ ceramics also have outstanding dielectric properties.At the same time,theε_r value and the volume density show an extremely similar change trend.The LBSCA glass could effectively reduce the sintering temperature to 1000℃.And,the excellent dielectric properties were obtained for the sample with 0.5 wt.%of LBSCA glass:ε_r=20.6,Q×f=69000GHz,τ_f=-57.33ppm/℃.（3）The BaCu（B₂O₅）material significantly reduced the sintering temperature of MgNb₂O₆ceramics while also increased the dielectric loss.The bulk density of MgNb₂O₆ ceramics is the main factor affecting theε_r,and theτ_f value of MgNb₂O₆ ceramics increases with the increase of BCB doping amount.When the addition amount is 1.5 wt.%,ceramic samples sintered at 900℃obtained the maximum microwave properties:ε_r=18.8,Q×f=35188GHz,τ_f=-42.72ppm/℃.On the basis of MgNb₂O₆+1.0 wt.%LMZBS,two kinds of materials（BaTi O₃,SrTi O₃）with higher positive temperature coefficient to adjust theτ_f value of MgNb₂O₆ceramics.The effects of the BaTi O₃ and SrTi O₃ addition on the phase composition,microstructure,density and dielectric properties were discussed systematically.The experimental data show that:（1）Doped BaTi O₃ could effectively adjust theτ_f value of MgNb₂O₆ material and when the content of BaTi O₃ is 15 wt.%,the good dielectric properties of composite ceramics were obtained:ε_r=20.9,Q×f=7500GHz,τ_f=-3.22ppm/℃.（2）Doped SrTi O₃ could effectively also adjust theτ_f value of MgNb₂O₆ ceramics.When the doping content of SrTi O₃ is 6 wt.%,the excellent dielectric properties of the ceramic material were achieved:ε_r=21.5,Q×f=20600GHz,τ_f=-2ppm/℃.