Investigation On The Microwave Dielectric Performance And Low Temperature Sintering Of Li₂Mg₄TiO₇ Ceramics

In pace with the rapid progress of microwave telecommunication and satellite broadcasting,microwave dielectric ceramics have been paid much attention for their potential electronic component applications in circuits.A novel low loss microwave dielectric ceramics Li₂Mg₄TiO₇ has been developed and studied for the first time based on the current research trends of microwave dielectric ceramics.The effects of sintering temperature on the phase composition,microstructure and microwave dielectric properties of the samples were systematically investigated.Meanwhile,a variety of divalent ion-doped were used to modified the microwave dielectric properties for Li₂Mg₄TiO₇ ceramics.In order to meet the requirements for LTCC applications,low-temperature sintering of Li₂Mg₄TiO₇ ceramics were also studied.Firstly,the novel ultra-low loss Li₂Mg₄TiO₇ microwave dielectric ceramics were successfully prepared by the conventional solid-state method.The relationships among sintering behavior,phase composition,microstructure and microwave dielectric properties of Li₂Mg₄TiO₇ ceramics were systematically investigated.In addition,the intrinsic factors that affected microwave dielectric properties were characterized using far-infrared spectroscopy,the results indicated that the dielectric constant of Li₂Mg₄TiO₇ was mainly affected by the polar optical phonons.Typically,the Li₂Mg₄TiO₇ ceramics sintered at 1600°C for 4 h exhibited excellent microwave dielectric properties with Q·?=158,250 GHz,ε_r=13.95 and?_?=-9.53 ppm/°C.Secondly,in order to improve the microwave dielectric properties of the Li₂Mg₄TiO₇ceramic,effort was now directed toward using different divalent ion substituted in Mg-sites to improve the dielectric properties of Li₂Mg₄TiO₇ ceramics.The Li₂(Mg_0.9A_0.1)₄TiO₇(A=Ca²⁺,Zn²⁺,Ni²⁺,Co²⁺)ceramics were separately prepared by the traditional solid-state method.The effects of different divalent ions on the microwave dielectric properties of the materials were systematically studied.The ceramics doped with Zn²⁺enhanced the quality factor Q·?values of the Li₂Mg₄TiO₇ ceramic within a certain range.A best microwave dielectric performance occupied withε_r=14.77,Q·?=162,200 GHz and?_?=-4.3 ppm/°C were obtained for Li₂(Mg_0.9Zn_0.1)₄TiO₇ ceramic when the samples sintered at 1500°C for 4 h.The ceramics doped with Ca²⁺significantly increased the dielectric constantε_r values and improved the temperature coefficient of the resonant frequency?_?.Additionally,high performance of microwave dielectric properties occupied withε_r=15.79,Q·?=100,300 GHz and?_?=-1.43ppm/°C could be obtained in the Li₂(Mg_0.9Ca_0.1)₄TiO₇ ceramics when the ceramics sintered at1300°C for 4 h.Finally,in order to achieve the co-fired requirements with silver and copper electrodes,LiF was chosen as the sintering aids to lower the sintering temperature of Li₂Mg₄TiO₇ceramics in the present study.Li₂Mg₄TiO₇ ceramics doped with 1-5 wt%LiF were successfully prepared by the conventional solid-state method.The sintering behaviors,phase compositions,microstructure and microwave dielectric properties of ceramics were associated with the sintering temperature and the amount of LiF addition.The Li₂Mg₄TiO₇ ceramics doped with 2 wt%LiF sintered at 950°C for 4 h possessed promising microwave dielectric properties withε_r value of 14.43,Q·f value of 48,700 GHz and?_fvalue of-3.83 ppm/°C,which showed that the materials were suitable for low-temperature co-fired ceramics（LTCC）applications.