Study On The Properties Of Mg (Subcomponents) Nb ₂ 9 Ceramics By Reaction Sintering Method And Their Microwave Dielectric Properties

With the rapid development of information technology, microwave dielectric ceramics put forward higher requirements, in order to meet the requirements of microwave devices, preparation of high-performance microwave dielectric ceramics has become an important research topic. The three main parameters to measure the performance of microwave dielectric ceramics, which should have a high quality factor (Qx f value), the appropriate dielectric constant (εr value), and the temperature coefficient of resonant frequency close to zero τf value). However, the ceramic has excellent microwave performance its sintering temperature is usually very high, thus reducing the sintering temperature and looking for new materials become an urgent problem.This paper selected Mg4Nb2O9ceramics for the study, its microwave dielectric properties is very excellent and preparation by the reaction-sintering process, and by adding B2O3to reduce the sintering temperature. The preparation of ceramic was researched, the phase composition and micro structure of the ceramic were characterized by XRD and SEM, and network analyzer was used to study microwave dielectric properties. The main contents are as follows:Mg4Nb2O9ceramics were prepared from Mg(IH)2and Nb2O5mixtures by using the reaction-sintering process for12h and the single phase Mg4Nb2O9was obtained at the sintering temperatures range of1200℃to1450℃. The apparent densities, Q×f and εr values revealed the similar tendency which changed with the sintering temperatures. The maximum density4.13g/cm3(relative density of94.25%) was obtained for Mg4Nb2O9sintered at1400℃, and the Mg4Nb2O9ceramic showed excellent properties:εr=12.1,Q×f=169000GHzandτf=-55.5ppm/℃.The results showed that the reaction-sintering process achieved dense, pure and high Q×f values Mg4Nb2O9ceramics, and that is a simple and effective method.Mg4Nb2O9ceramic with x mol%(x=0、1、2、3、4、5) excess Mg(OH)2was synthesized by reaction-sintering process, and research the excessive Mg(OH)2affect the performance of Mg4Nb2O9ceramics. At sintering temperatures range of1200℃to1450℃the main phase is Mg4Nb2O9, and a small amount of MgO phase. The apparent densities, Q×f values and εr values revealed the similar tendency. Observation of SEM photographs found that with the increasing of Mg(OH)2content, hardly observed porosity on ceramic surface and uniform distribution. The maximum density4.22g/cm3was obtained for Mg4Nb2O9sintered at1400℃with3mol%excess Mg(OH)2added, and the Mg4Nb2O9ceramic showed excellent microwave dielectric properties:εr=12.6, Q×f=196700GHz and τf=-47.3ppm/℃. The performance of ceramic increased than stoichiometric ratio.Synthetization B2O3doped Mg4Nb2O9ceramic by the reaction-sintering process. Mg4Nb2O9ceramic with ywt%B2O3(y=0.5、1.0、1.5、2.0、2.5、3.0) ceramics excess3mol%Mg(OH)2was synthesized. The sintering temperatures range from1100℃to1250℃, and the main phase is Mg4Nb2O9, and a small amount of MgO phase. The diffraction peak of Mg4Nb2O9ceramics shift to lower angle with the increase of B2O3. The maximum density3.94g/cm3was obtained for Mg4Nb2O9-2.0wt%B2O3sintered at1200℃, and the Mg4Nb2O9-2.0wt%B2O3ceramic showed excellent properties: εr=12.0,Q×f=156400GHz and τf=-51.0ppm/℃. The sintering temperature of Mg4Nb2O9-ywt%B2O3ceramics is reduced about200℃. It is beneficial to reduce the sintering temperature by doping appropriate amount of B2O3.