Microwave Dielectric Properties And Low Temperature Sintering Of Li₂Mg₃Ti_1-x(Mg_1/3Nb_2/3)_xO₆ Ceramics

With the development of the wireless communication system,there is a higher demand for microwave dielectric materials.As a key material for electromagnetic wave transmission and processing in microwave frequency circuits,microwave dielectric ceramics have attracted much attention.Li₂Mg₃TiO₆ based microwave dielectric ceramics are potential materials because of their low dielectric constant and excellent quality factor.However,for low dielectric constant microwave dielectric ceramics,the optimization of quality factor and low temperature sintering research are still urgent problems to be solved.Li₂Mg₃Ti_1-X(Mg_1/3Nb_2/3)_XO₆?0?x?0.25?ceramics were prepared by a conventional solid-state reaction process.The effect of(Mg_1/3Nb_2/3)⁴⁺ion doping on the structure,microwave dielectric properties were studied.As the doping amount increases,no second phase was found,pure rock-salt structure was synthesized according to XRD.Dense structure and uniform grain size were obtained for samples sintered at 1550?,while the microwave dielectric properties were dominated by intrinsic factors.The P-V-L chemical bond theory,polarizability,Raman spectroscopy,bond strength and bond valence were investigated.The results indicated that the?_r decreases as the?/V_m and crystal ionicity;quality factor was related to intrinsic loss which could be characterized by FWHM of Raman spectrum,the intrinsic loss decreases with increasing lattice energy;the decrease in?_?values was due to the decrease in bond strength,the coefficient of thermal expansion and bond valence were opposite to?_?values.Excellent microwave dielectric properties of?_r=14.79,Q·f=204,000GHz and?_f=-18.43 ppm/? were obtained for Li₂Mg₃Ti_0.95(Mg_1/3Nb_2/3)_0.05O₆ ceramic sintered at 1550?.However,the higher sintering temperature limits industrial production and application field of Li₂Mg₃Ti_0.95(Mg_1/3Nb_2/3)_0.05O₆ ceramics.In this work,LiF is choose as sintering aids to reduce the sintering temperature of the ceramic.The effect of LiF doping on Li₂Mg₃Ti_0.95(Mg_1/3Nb_2/3)_0.05O₆ sintering temperature and microwave dielectric properties were studied.The phase composition,sintering characteristics,micro-morphology and microwave dielectric performance were analyzed.The doping of 3-5wt.%Li F can effectively reduce the sintering temperature,and samples sintered at 1000?can achieve well densification.The Li₂Mg₃Ti_0.95(Mg_1/3Nb_2/3)_0.05O₆ doped with 3wt.%LiF ceramics exhibited an uniform grain size and no obvious pores at 1000?,and optimal microwave dielectric performance of?_r=14.95,Q·f=117,000 GHz and?_f=-11.21 ppm/? were obtained.