A Site Ion Substitution Of Mg 2 Of SiO . 4 Preparation And Microwave Dielectric Properties Of The Regulation Based Ceramics

With the rapid development of modern information technology, especially the rapid development of mobile communications, miniaturization and lightweight of microwave devices have been increasingly addressed, preparation of high-performance microwave dielectric ceramics has become an important research topic. Magnesium silicate ?Mg₂SiO₄? ceramic is expected to become a newly developed of high Q value microwave dielectric substrate material, due to its high Q×f value and low ?r. However, Mg₂SiO₄ has the characteristics of high sintering temperature and difficult to compact, which limit its applications in commercial. At present, the microwave dielectric ceramics are developing in high frequency components, low-temperature co-fired. Thus, it is worth to lower the sintering temperature and improve the microwave dielectric properties of magnesium silicate ceramics.In this thesis, effects of composition and sintering temperature upon the sintering characteristics, phase components, microstructure and microwave dielectric properties of Mg₂SiO₄ ceramics were investigated. Firstly, we designed experiments and obtained the pure phase Mg₂SiO₄ according to a large number of materials document has been referenced. Moreover, Ca substitution for Mg, Cu substitution for Mg, and LiF co-doped were conducted to lower the sintering temperature of Mg₂SiO₄ ceramics; modification of microstructure and microwave dielectric properties were conducted by ?La0.5Na0.5?TiO3 addtion. The principal experiment results were shown as follows:?1? Mg₂SiO₄ ceramic with x mol%?x= 0,2,4,6? excess MgO was synthesized by the conventional solid-reaction method, and the excessive MgO on the performance of Mg₂SiO₄ ceramics were investigated. The samples were detected by X-ray diffraction, and the pure Mg₂SiO₄ was synthesized when x= 0 mol%, however, samples with 2,4, 6 mol% excess MgO display Mg₂SiO₄ phase accompanying with a little amount of MgO phase. The influence of sintering temperature and microstructure on Mg₂SiO₄ ceramics was researched by the comparison of the results. The results indicate that specimens with x= 0 mol% sintered at 1560? reache a maximum relative density of 98.5%, the grain size of 4.0?6.0 ?,m and well microwave dielectric properties:?r= 7.8, Qxf= 211,000 GHz, ?f=-61 ppm/?.?2? With Ca²⁺ substitution for Mg²⁺, ?Mg1-xCax?2SiO4?0.01? x? 0.06? ceramics were fabricated and their structural characteristics, sintering behavior, and microwave dielectric properties were investigated. The results revealed that solid solution was formed at x? 0.04 and the sintering temperature of Mg₂SiO₄ ceramics was lowered from 1560? to 1310?1390?, however, the grain size of Mg₂SiO₄ ceramics was not changed obviously. As a result, a ?r value of 7.8 and Q×f value of 115 000 GHz with a ?f value of -68 ppm/? were obtained for the ?Mg0.08Ca0.02?2SiO4 ceramics sintered at 1370? for 4h.?3? With Cu²⁺ substitution for Mg²⁺, Mg2-xCuxSiO4 ?0.01?x?0.2? ceramics were fabricated and their structural characteristics, sintering behavior, and microwave dielectric properties were investigated. The results indicate that solid solution was formed for x?0.2, and the substitution could effectively promate grain growth and lower the sintering temperature from 1560? to 1200?. The Mg1.9Cu0.1SiO4 ?MCS? ceramic sintered at 1200? for 4h and displays excellent microwave dielectric properties of ?r= 7.6, Q×f= 63,300 GHz, and ?f=-54 ppm/?. Furthermore,4 wt% LiF-doped ?1-y? Mg1.9Cu0.1SiO4-y ?La0.5Na0.5?TiO3 ??1-y? MCS-y LNT,0.1?y? 0.4? composite ceramics were produced and their microwave dielectric properties also were investigated. As increasing LNT content y, the ?f values showed a continuous positive increase. The 0.8 MCS-0.2 LNT composite ceramics with 4.0 wt% LiF sintered at 950? for 4h possess excellent microwave dielectric properties of ?r= 13.3, Q×f= 14,400 GHz, and ?f-6 ppm/?. The low-temperature sintering ceramics are suitable for the LTCC application.