| With the rapid development of microwave communication devices and the demand for mobile 5G communication,medium dielectric constant ceramic along with high quality factor,as the key material for mobile base station,are attracting more and more attentions.However,At present,several high quality factor and medium dielectric constant practical ceramics has been reported,but their sintering temperature beyond 1500? will lead to more energy consumption and higher costs in industrial production.Thus it is significant to research and develop microwave dielectric materials with high quality factor,moderate dielectric constant and relatively lower sintering temperature.ZnTiNb2O8 ceramics with a manganese tantalum structure can be sintered at 1120? and has good microwave dielectric properties(?r=34.4,Q×f=56900 GHz,?f-47.94×10-6/?).However,the high negative value of the resonant frequency temperatule coefficient hinders its practical application.At present,most of the studies on ZnTiNb2O8 ceramics at home and abroad have focused on substitution modification of one type of ion,which often led to a significant reduction or even deterioration of the Qxf value while improving ?f Moreover,the preparation process parameters adopted by different researchers were different and lacked certain contrast.Therefore,in this dissertation,ZnTiNb2O8 microwave dielectric ceramics were chosen as research object;to obtain the best preparation process parameters,the influence of the preparation process parameters on microstructure and microwave dielectric properties of ZnTiNb2O8 ceramics were systematicly investigated;Then,appropriate Ti position ion was selected to improve the quality factor of material.Finally,a suitable type of ion was selected to replace Zn2+ to adjust the resonant frequency temperature coefficient of materials and to obtain excellent microwave dielectric properties of materials.Firstly,the effects of preparation technology about ZnTiNb2O8 microwave dielectric ceramics have been investigated and the effects of the calcining temperature,sintering temperature and holding time on phase composition,bulk density,microstructure and microwave dielectric properties was discussed,respectively.The results showed that the best microwave dielectric properties of ZnTiNb2O8 ceramics with relative density of 98.5%was ?r=36.72,Q×f=47689 GHz,?f=-75.96x10-6/? when calcined at 900? and sintered at 1100? for 6 h.Secondly,the effects of Zr4+substitution for Ti4+on phase composition,bulk density,microstructure and microwave dielectric properties of Zn(Ti1-xZrx)Nb2O8(x=0-0.6)ceramics were investigated.The results showed that a single phase ZnTiNb2O8 with manganese tantalite structure was formed when x was less than 0.4;while a single phase ZnTiNb2O8 with wolframite was formed when x exceeded 0.4;the amount of Zr4+substitution had a significant influence on microstructure of ZnTiNb2O8 ceramics.With the increase of bulk density decreased,the average grain size decreased and tended to uniform distribution.ZnTi0.6Zr0.4Nb2O8 ceramics sintered at 1120? for 6 h displayed uniform and smooth morphology,and the best microwave dielectric properties of ?r=33.43,Qxf-59475 GHz,?f=76.54X 10-6/? could be obtained.Finally,Ca2+substitution for Zn2+ was adopted to adjust the resonant frequency temperature coefficient of Zn(Ti0.6Zr0.4)Nb2O8 ceramics.The effect of Ca2+substitution amount on phase composition,bulk density,microstructure and microwave dielectric properties of(Zn1-xCax)(Ti0.6Zr0.4)Nb2O8(x=0.05-0.3)ceramics were investigated.The results showed that the replacement of Zn2+by Ca2+ leaded to the formation of secondary phase CaNb2O6.With the increase of Ca2+content,the content of ZnTiNb2O8 phase decreased and the content of CaNb2O6 phase increased,which resulted in decrease in bulk density,quality factor and relative dielectric constant,and the temperature coefficient of the resonant frequency moved towards the positive direction.The best microwave dielectric properties were obtained for(Zn1-xCax)(Ti0.6Zr0.4)Nb2O8 ceramics(x=0.3)sintered at 1140? for 6 h:?r=30.42,Q×f47280 GHz,?f=-25.37×10-6/?. |
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