Preparation And Study Of Nano-sized Li₂O-TiO₂by A Sol-gel Method And Its Microwave Dielectric Properties

With the rapid progress in mobile telecommunication, wireless local area network(LAN) and military radar technologies,it has been strongly required that the related components become light-waighted, small-sized, light-waighted, multifunctional and usable at higher frequency range. In order to fulfill these requirements. The dielectric ceramics with low or moderate dielectric constant, together with design and fabrication of multilayer chip microwave components using low temperature co-fired ceramics (LTCC) technology has become a research focus in recent years.Li2TiO3ceramics exhibit moderate dielectric constant,high quality factor, et cetera. This material systems could be promising LTCC materials if they can sintered at low temperature and compatible with LTCC technology. Recently, some works on microwave dielectric properties based on Li2TiO3material systems have been reported,but still some tough problems remain as follows:(1) it’s difficult to decrease the sintering temperature and the microstructure of ceramic can be impaired due to the pores and cracks caused by Li evaporation and phase transition at high temperature.(2)Though the sintering temperature of dielectrics was decreased lower than950℃, dielectric properties of Li2TiO3ceramics doped with B2O3-ZnO glass additives showed inhibited improvement in quality factor values:32300GHz.In this investigation, Li2TiO3nanoparticles with small size and narrow size distribution were synthesized by sol-gel method. Besides the effect of a slight cation nonstoichiometry and the addition of LiF as sintering aid on the structure, densification and microwave dielectric properties of Li2TiO3were investigated.Ultrafine Li2TiO3nanoparticles with particle size under20nm were synthesized at the first time by a sol-gel method. The effect of a slight cation nonstoichiometry on the structure, densification and microwave dielectric properties of Li2TiO3was investigated. The phase presence and surface morphology were determined by XRD and SEM techniques, respectively. The average particle size calculated from the TEM micrograph of the powder was6-12nm. Compared with the conventional solid-state method, Li2TiO3nanopowder synthesized by the sol-gel method could be densified at1250℃with less micro pores and cracks. The Li2TiO3ceramics prepared from nanoparticles can achieve a density of93%which induced the enhanced microwave properties.Besides, the densification temperature of a slightly A-site nonstoichiometric ceramics has been successfully reduced to1050"C. The ceramic sintered at1050℃with0.08excessive Li exhibit a well-defined micro structure and high density of96%. The ceramic possess an improved microwave property compared with those prepared from solid-state method:εr=23.2, Q×f=56400GHz and τf=38.4ppm/℃Also, it is found that a slight cation defect can improve density and microwave dielectric properties, while the addition of excesss ions deteriorated them.In addition, LiF was added as sintering aid to reduce the sintering temperature of Li2TiO3ceramics for LTCC application, and well-densified microwave ceramics with uniform grains could be obtained under950℃. Typically, optimum dielectric microwave of εr=24.01, Q×f=75500GHz, and τf=36.2ppm/℃was achieved for2.5wt%LiF doped samples sintered at950℃for3h. The chemical compatibilities of2.5wt%LiF doped ceramics with silver were also investigated. The low-temperature sintering ceramics are compatible with Ag electrodes, and therefore, suitable for low-temperature co-fired ceramics (LTCC) application.