Research On Microwave Dielectric Properties Of Li₂Mg₃TiO₆ Ceramics With The Lower Sintering Temperature

Due to the excellent microwave dielectric properties,Li₂Mg₃TiO₆ceramics had caught increasingly attention.However,its sintering temperature may reach 1300℃,which hindered its application in actual production and LTCC technology.In this paper,the low temperature sintering characteristics and microwave dielectric properties of Li₂Mg₃TiO₆ceramics were investigated comprehensively.The main research content is as follows:（1）The sintering characteristics and microwave dielectric properties of Li₂Mg₃TiO₆ceramics with different content of LiF were reachered.The liquid phases were formed during sintering,which promotes the densification of ceramics and reduces the sintering temperature below 950℃.Finally,Li₂Mg₃TiO₆-4wt%ceramics sintered at 900℃ have the excellent dielectric properties:?_r～15.64,Q×f～136,000GHz,τ_?～-34.5ppm/℃.（2）To improve the Q×f value of Li₂Mg₃TiO₆-4wt% ceramics,the B-site of Ti⁴⁺ions were substituted by the complex ions of(Al_1/2Nb_1/2)⁴⁺and(Mg_1/3Nb_2/3)⁴⁺.The solid solution limit of(Al_1/2Nb_1/2)⁴⁺ions in Li₂Mg₃TiO₆-4wt%LiF ceramics is0.04mol.When the substitution amount of(Al_1/2Nb_1/2)⁴⁺ions was 0.04mol,the occupancy of Ti⁴⁺ions was replaced and the degree of lattice distortion reaches a maximum in the crystal structure,which promoted the sintering process significantly.Therefore,the Q×f value of Li₂Mg₃TiO₆-4wt%ceramics was improved from136,000GHz to 154,000GHz effectively.However,when the substitution amount is more than 0.04mol,the second phase Mg AlO₄could be formed,which has a negative influence on the dielectric properties.For the Li₂Mg₃Ti_0.9(Mg_1/3Nb_2/3)_0.1O₆-4wt%LiF ceramics,good microwave dielectric properties of ?_r～15.66,Q×f～140,000GHz,τ_?～-40.5ppm/℃ were obtained at the sintering temperature of 925℃.（3）The crystal structure and microwave dielectric properties of Li₂Mg₃Ti_1-xSn_xO₆（0.02≤x≤0.08）ceramics were investigated.The crystal structure and unit cell volume of samples were obtained by Rietveld refinement.The relationship between the corrected dielectric constantε_corr andε_r,the relationship between lattice vibration and Q×f value,and the trend ofτ_?value were analyzed.The superior dielectric properties of?_r～13.16,Q×f～168,800GHz,τ_?～-29.8ppm/℃ were obtained for Li₂Mg₃Ti_0.94Sn_0.06O₆ ceramics sintered at 1350℃.Furthermore,LiF was added to Li₂Mg₃Ti_0.94Sn_0.06O₆ ceramics to lower the sintering temperature.The excellent dielectric properties of?_r～15.58,Q×f～142,210GHz andτ_?～-34.5ppm/℃ for Li₂Mg₃Ti_0.94Sn_0.06O₆-3wt%LiF ceramics were obtained sintered at 900℃.（4）LiF was added before calcination to study the change of sintering temperature and dielectric properties by F^-ion substituted O^2-ion for Li₂Mg₃TiO₆ ceramics.The calcining temperature could be reduced from 1000℃ to 700℃ attributed to the introduction of crystal defects and the decrease of the chemical potential and free energy.What’s more,the optimum sintering temperature was reduced gradually as F^-ions increased for Li₂Mg₃Ti(O_1-x/2F_x)₆（0.06≤x≤0.15）ceramics.The Li₂Mg₃Ti(O_0.96F_0.08)₆ ceramics calcined at 700℃ and sintered at 950℃ for 6 hours exhibited the excellent microwave dielectric properties of?_r～14.57,Q×f～92,450GHz andτ_?～-32.91ppm/℃.Furthermore,The Q×f value of Li₂Mg₃Ti(O_0.96F_0.08)₆ ceramics was improved by replacing Mg²⁺ions with Zn²⁺ions.When the substitution amount was 0.02mol,the Q×f value was increased to 128,000GHz.