Novel AO-TiO₂-Ta₂O₅(A=Mg²⁺,Mn^{2 Preparation Of +}) Ceramics And Their Microwave Dielectric Properties

In recent years,with the rapid development of mobile communications and the advent of the 5G era,people have put forward higher requirements for the miniaturization of microwave devices,which urgently requires microwave dielectric materials must have a high Q xf value(Q xf>5000 GHz),a medium and high dielectric constant(?r>10),and a near-zero temperature coefficient of resonant frequency(rf?0 ppm/?).In this thesis,two new types of tantalitebased microwave dielectric ceramics with good performance were developed by using solidstate reaction method,and their microwave dielectric properties were optimized by two-phase composite and ion substitution methods.Some valuable results were obtained:(1)The MgTiTa2O8 ceramics were fabricated by the conventional solid-state reaction method,and their microwave dielectric properties were studied.The MgTiTa2O8 ceramics were well sintered over the temperature range(1150??1300?),achieving the optimized density(-95%)at 1225?.X-ray diffraction and its Rietveld refinement results confirmed that MgTiTa2O8 ceramics crystallized into a trirutile-type structure with space group P42/mnm(No.136).The MgTiTa2O8 ceramic sintered at 1225? exhibited the optimized dielectric properties with relative permittivity of 41.6,Q×f value of 30000 GHz,and ?f value of+104 ppm/?.(2)xMgTiTa2O8-(1-x)MgMoO4(x=0,0.1,0.2,0.25,0.3)composite ceramics were prepared by conventional solid-state reaction method,and excellent microwave dielectric properties with ?f near zero were obtained.The effects of different doping contents of MgMoO4 on phase composition,sintering behavior and microwave dielectric properties of ceramics were studied.In the temperature range of 950 ??1100?,the composite ceramics contained only two structures:the trirutile structure MgTiTa2O8 and the monoclinic structure MgMoO4,and the optimal sintering temperature moved to low temperature with increasing MgMoO4 content.0.25MgTiTa2O8-0.75MgMoO4 ceramic sintered at 1000? obtained the best microwave dielectric properties with ?r?10.8,Q×f value?30000 GHz and near-zero temperature coefficient ?f?-5.7 ppm/?.(3)Mg(Ti1-xZrx)Ta2O8(x=0,0-05,0.1,0.3,0.5,0.7,0.9,1.0)ceramics were fabricated by conventional solid-state reaction method.The phase composition,sintering behavior and microwave dielectric properties were investigated as a function of the content of Zr4+.The phase structure of the Mg(Ti1-xZrx)Ta2O8(x=x?1)ceramic system was divided into three regions:trirutile phase solid solutions were observed when x ? 0.3;monoclinic wolframite phase coexisted with trirutile phase when x=0.5,and the content ratio was about 95:5;when x? 0.7,the ceramic samples formed monoclinic MgZrTa2O8 phase solid solutions.With the increase of Zr4+content,the optimal sintering temperatures of Mg(Ti1-xZrx)Ta2O8(x=0?1)ceramics also increased,dielectric constant(?r)changed from 42 to 18 and temperature coefficient of the resonant frequency(?f)shifted from+98.6 ppm/? to-24.3 ppm/?.Among them,the twophase coexistence region(x=0.5)and the monoclinic MgZrTa2O8 phase solid solution region(x?0.7)can adjust the temperature coefficient to zero.In the two-phase coexistence region,when the Zr4+subsititution amount reached 0.5,the Mg(Ti0.5Zr0.5)Ta2O8 ceramic sintered at 1350? showed excellent microwave dielectric properties:?r?24.6,Q×f?39000 GHz and ?f?-28.2 ppm/?.(4)The new type MnO-TiO2-Ta2O5 microwave dielectric ceramic was fabricated by conventional solid-state reaction method.The effects of different sintering temperatures on the phase composition,sintering behavior and microwave dielectric properties of MnO-TiO2-Ta2O5 ceramics were studied.It was found that the as-fabricated ceramics sintered at 1150??1350? all have relatively dense micro structures,which are all composed of two phases:monoclinic Mn1.333Ta2.667O8 and tetragonal Ti0.51Tao.49O2.MnO-TiO2-Ta2O5 ceramics obtained at 1250?have excellent microwave dielectric properties:?r?31,Q×f21100 GHz;?f?-53 ppm/?.The development of MnO-TiO2-Ta2O5 ceramics has enriched the microwave dielectric material system in the range of medium dielectric constant.