Preparation And Properties Of Mg₂TiO₄-based Microwave Dielectric Ceramics

The spinel structure material Mg₂TiO₄ has attracted much attention of researchers at home and abroad,because of low dielectric constant??_r¹4?,low dielectric loss?Q×f¹50000 GHz?,low cost and abundant raw material source.However,Mg₂TiO₄ microwave dielectric ceramic has some disadvantages such as too high sintering temperature,large negative?_f and difficult to prepare pure phase,which affect the practical application.In this paper,Mg₂TiO₄ microwave dielectric ceramic was chosen as research object,the pure phase Mg₂TiO₄ with appropriate process parameters was studied.The phase composition,microstructure and microwave dielectric properties of Mg₂TiO₄-based microwave dielectric ceramic have been investigated systematically by the ways such as two phase composite,ion doping and adding sintering additives.The main research contents are as follows:1.The pure phase Mg₂TiO₄ powder was prepared by the traditional solid state reaction method.The effects of raw material ratio,milling time,calcination temperature and time on the calcined powder were studied.The optimum conditions were as follows:Mg/Ti was 2.02,the milling time was 14h,the calcination temperature was 1190?and the calcination time was 4h.It was found that pure phase Mg₂TiO₄ ceramics had the plate microstructure,and its microwave dielectric properties were closely related to its density.When Mg₂TiO₄ ceramic was sintered at1475?for 4h,the ceramic had the best microwave dielectric properties:?_r=14.6,Q×f=156000 GHz,?_f=-49.9 ppm/?.2.Ca_0.8Sm_0.4/3TiO₃ was used to adjust the frequency temperature coefficient of Mg2TiO4 ceramic.The effects of the addition of composite on the phase composition,microstructure and microwave dielectric properties of Mg₂TiO₄ ceramic were studied.It was found that the addition of Ca_0.8Sm_0.4/3TiO₃ inhibited the plate microstructure of pure phase Mg₂TiO₄ ceramic,which promoted the sintering of Mg₂TiO₄ ceramics and reduced the sintering temperature of Mg₂TiO₄ ceramics from 1475?to 1375?.When the concentration of Ca_0.8Sm_0.4/3TiO₃ was 17wt%,the microwave dielectric properties of the composite ceramics sintered at 1375?for 4h:?_r=19.7,Q×f=37060 GHz,?_f=+1.0 ppm/?.The Sn⁴⁺doping modification of 0.83Mg₂TiO₄-0.17Ca_0.8Sm_0.4/3TiO₃ ceramic was studied.The results showed that a small amount of Sn⁴⁺doping can optimize the microwave dielectric properties of ceramics.When the doping amount of Sn⁴⁺is 0.03,the composite ceramic exhibited good microwave dielectric properties sintered at 1350?for 4h:?_r=19.4,Q×f=40880GHz,?_f=+1.1ppm/?.3.The sintering behavior of 0.83Mg₂TiO₄-0.17Ca_0.8Sm_0.4/3TiO₃ ceramic was studied by adding sintering aids B₂O₃.B₂O₃ exited in specimen in the form of liquid phase.An appropriate amount of B₂O₃ can promote the ceramic densification,lower the sintering temperature and do not deteriorate the microwave dielectric properties.When the addition amount of B₂O₃ was 3wt%,the ceramic sintering temperature was reduced by 75?,and the composite ceramic sintered at 1300?for 4h had microwave dielectric properties:?_r=19.8,Q×f=38710 GHz,?_f=+0.4 ppm/?.The appropriate amount of LiF is beneficial to the densification of ceramic.Mixing with B₂O₃,multicomponent sintering agents B₂O₃-LiF were more effective than single B₂O₃ to lowering the sintering temperature of 0.83Mg₂TiO₄-0.17Ca_0.8Sm_0.4/3TiO₃ceramic with the microwave dielectric properties of the ceramic optimized.When x=1.5 with the addition of LiF was 1.5wt%,the ceramic had excellent microwave dielectric properties at 1250?for 4h:?_r=18.3,Q×f=46390 GHz,?_f=-0.2 ppm/?.4.SrTiO₃ was used to adjust the frequency temperature coefficient of Mg₂TiO₄ceramic.It was found that the addition amount of SrTiO₃ had a significant effect on the adjustment of the frequency temperature coefficient of Mg₂TiO₄ ceramics and promoted the sintering of Mg₂TiO₄ ceramics.When x=0.08 with the addition amount of SrTiO₃ is 8wt%,the composite ceramic had excellent microwave dielectric properties at 1375?for 4h:?_r=17.2,Q×f=61130 GHz,?_f=-5.8 ppm/?.