Structure Analysis And Properties Study Of Low Dielectric Constant And Low Loss Li₃Mg₂NbO₆ Series Microwave Dielectric Ceramics

Li₃Mg₂NbO₆ ceramic is a new type of low dieletcric constant and low-loss microwave dielectric material discovered in recent years,but it has a relatively low Q×f value and a small negativet_f value,which makes it unable to meet the practical application requirements.In this paper,the non-stoichiometric ratio of A-site ions is used to compensate the lithium volatilization phenomenon caused by high temperature sintering of Li₃Mg₂NbO₆ ceramics,thereby improving properties of ceramics.In addition,Nb⁵⁺in Li₃Mg₂NbO₆ ceramics was replaced by hexavalent ions and pentavalent composite ions,and the properties and influencing factors were also studied.1.Li₃Mg₂NbO₆ phase ceramics were successfully prepared by non-stoichiometric ratio of A-site ions,and the obtained ceramic samples were analyzed for structure and microwave dielectric properties.The results show that the use of non-stoichiometric ratio Li⁺can compensate for the volatilized lithium during high-temperature sintering.The non-stoichiometric ratio Mg²⁺can fully react with Li⁺which is less than the normal stoichiometric ratio after volatilization,thus avoiding the formation of Mg O miscellaneous phase.Increasing the content of Li⁺or reducing the content of Mg²⁺can effectively promote grain growth and reduce the porosity.In addition,the paper also systematically studied the effect of the non-stoichiometric ratio of the A-site ion on the lattice structure of the sample,and established the relationship between the lattice structure and the microwave dielectric properties of the sample.2.Li₃Mg₂(Nb_1-xMo_x)O_6+x/2 ceramics and Li₃Mg₂(Nb_1-xW_x)O_6+x/2 ceramics with excellent microwave properties were prepared by substituting hexavalent ions(Mo⁶⁺and W⁶⁺)for the B-site Nb⁵⁺in Li₃Mg₂NbO₆ ceramics.The effects of different hexavalent ions substitution on the structure and properties of Li₃Mg₂NbO₆ ceramics were investigated systematically.The results show that Li₃Mg₂(Nb_0.98Mo_0.02)O_6.01ceramics sintered at 1200℃ for 6h exhibite the best microwave dielectric properties,e_r～15.18,Q×f～116,266 GHz,t_f～-15.71 ppm/℃,and Li₃Mg₂(Nb_0.94W_0.06)O_6.03ceramics sintered at 1175℃ for 6h exhibite the best microwave dielectric properties,e_r～15.82,Q×f～124,187GHz,t_f～-18.28 ppm/℃.3.Using pentavalent complex ions((Li⁺/Ti⁴⁺),(Li⁺_1/5W⁶⁺_4/5)⁵⁺,(Mg²⁺_1/4W⁶⁺_3/4)⁵⁺,(Al³⁺_1/3W⁶⁺_2/3)⁵⁺and(Ti⁴⁺_1/2W⁶⁺_1/2)⁵⁺)replace Nb⁵⁺in Li₃Mg₂NbO₆ ceramics,respectively.Results have shown that the use of complex ions replacement would improve the overall performance of ceramics in many aspects.