Preparation And Investigation Of Li₂MgTiO₄ Based Microwave Dielectric Ceramics

With the rapid development of communications equipment,high frequency and high integration are more and more important,the microwave dielectric ceramic has attracted much scientific attention in the field of functional materials.In general,The microwave dielectric ceramic should meet three primary requirements to produce good performance:a high quality factor?Q×f?for achieving prominent frequency selectivity and stability,moderate dielectric constant??_r?,and near-zero temperature coefficient of resonant??f?to guarantee high temperature stability.Recently,microwave dielectric ceramic compounds based on Li₂O-MgO-TiO₂ have attracted attention for their low cost of the production,light weight,and great microwave dielectric properties.Among this system,Li₂MgTiO₄?LMT?with rock-salt-structure shows a proper dielectric constant and high quality factor,which makes them a suitable candidate for antenna.The influence of substitution and composition respectively on the crystal structure,micromorphology and microwave dielectric properties of Li₂MgTiO₄ceramic sample were discussed systematically.In this paper,Li₂MgTiO₄+x wt.%?x=5-9?CaTiO₃ microwave dielectric ceramics with high temperature stability were prepared by solid-state reaction.The results show that Li₂MgTiO₄ and CaTiO₃ phases coexist and the content of CaTiO₃ phase increases,the dielectric constant increases,whereas quality factor and temperature coefficient of resonant frequency decreases because of the increase of CaTiO₃ content.And the doping of CaTiO₃ can decrease sintering temperature.The Li₂MgTiO₄+6 wt.%CaTiO₃ ceramics sintered at 1210°C for 4 h show great properties:?_r=18.03,Q×f=69,022?at 7.886 GHz?,?f=-3.03 ppm/°C.The effects of non-stoichiometric ratio on crystal phase structure,microstructure and microwave dielectric properties of Li_?2+x?MgTiO₄?x=0.00,0.04,0.08,0.12?ceramic were investigated.The crystal phases of Li_?2+x?MgTiO₄ stay the same as a function of x value.And the microwave dielectric properties of Li_?2+x?MgTi O₄ improve a little at the first and then decrease with the further increase of x.The Li_2.04MgTiO₄ ceramics sintered at1210°C for 4 h show great properties:?_r=17.01,Q×f=89877?at 7.887 GHz?,?f=-31.56ppm/°C?Influence of ionic substitution on the microwave dielectric properties of Li₂Mg_0.95R_0.05TiO₄?R=Cu,Zn,Co,Mn?was investigated.The crystal phases of Li₂Mg_0.95R_0.05TiO₄?R=Cu,Zn,Co,Mn?stay the same.and the temperature coefcient of resonant frequency showed no signifcant changes with the ionic substitutions.For R=Zn and Co,the quality factor of increases.The Li₂Mg_0.95Co_0.05TiO₄ ceramics sintered at1210°C for 4 h show great properties:?_r=17.16,Q×f=91121GHz,?f=-31.66 ppm/°C?Effectsof ionic substitution on the crystal phase structure,microstructure,microwave dielectric properties of Li₂MgTi_0.95R_0.05O₄?R=Zr,Sn,Mn,Cu?was studied.The crystal phases of Li₂MgTi_0.95R_0.05O₄?R=Zr,Sn,Mn,Cu?stay the same.The variation of dielectric constants was in related with that of apparent densities and theoretical polarizability.The poles of Li₂MgTi_0.95Cu_0.05O₄ microwave dielectric ceramics cause the decrease of their performance.The Q×f values were improved when Ti was substituted by Zn and Sn,At 1330°C,Li₂MgTi_0.95Sn_0.05O₄ possessed an excellent microwave dielectric property:Q×f=86851GHz,?f=-31.14 ppm/°C,?_r=16.48?...