Processing And Property Study Of Mg₂TiO₄ -based Microwave Dielectric Ceramics

Mg₂TiO₄-based ceramics are chosen as research objective in this dissertation. The best synthesis methods of Mg₂TiO₄ powder were investigated and different additives regulatingτ_f of Mg₂TiO₄ to zero were chosen to adjust Mg₂TiO₄ ceramics suitable for microwave communication application.By using traditional solid-phase synthesis method, the influence of calcining temperature and 1100°C-heated MgO on the sintering behavior and microwave dielectric properties of Mg₂TiO₄ powders and ceramics were investigated. The results shows that: the best calcining temperature is 1190°C and the Mg₂TiO₄ ceramics are porous, and Mg₂TiO₄ powders synthesized with non-heated MgO have better microwave dielectric properties and lower sintering temperature.In the following experiments, non-heated MgO was chosen to synthesis Mg₂TiO₄ powders, and the calcining temperature was setted as 1090°C. As Mg₂TiO₄-CaTiO₃ is difficult to be densified, by adding the second low temperatue melting oxide ZnNb₂O₆, the influence of ZnNb₂O₆ and CaTiO₃ on phase compositions, microstructures and microwave properties of Mg₂TiO₄ ceramics have been studied. The study found that a small amount of ZnNb₂O₆ can improve the density,εr and Q×f of Mg₂TiO₄-CaTiO₃ ceramics, and lower itsτ.Though SrTiO₃ could also adjust theτ_f of Mg₂TiO₄, the Mg₂TiO₄- SrTiO₃ ceramics is not suitable for practical usage because of their lowεr. So Ca0.8Sr0.2TiO₃ with high Q×f andτ_f was chosen to adjust Mg₂TiO₄ ceramics. By researching Mg₂TiO₄-Ca0.8Sr0.2TiO₃ system, we found that Ca/Sr in Ca0.8Sr0.2TiO₃ grains changed from 4 to 3. However, the reason needs further investigate. Moreover, Mg₂TiO₄ grains grew up rapidly with increasing sintering temperature, leading the sintering behavior of ceramics changed in high temperature:εr increased, however, Q×f andτ_f decreased with increasing sintering temperature. The reason for decreasingτ_f also needs further investigate.Finally, to increaseεr of Mg₂TiO₄, 0.01mol Co was added. Then Ca_0.8Sm_0.4/3TiO₃ with high quality factor was chosen to regulate theτ_f of (Mg_0.09Co_0.01)₂TiO₄. (Mg_0.09Co_0.01)₂TiO₄, Ca_0.8Sm_0.4/3TiO₃ and(Mg_0.09Co_0.01)TiO₃ phase and many pores exist in (1-x)(Mg_0.09Co_0.01)₂TiO₄-xCa_0.8Sm_0.4/3TiO₃ system, however, the grains size are much smaller than we investigated before, hence the whole microwave dielectric properties are much better. With increasing sintering temperature, (Mg_0.09Co_0.01)₂TiO₄ grains grows slowly, makingεr increase, while Q×f increase initially and decrease thereafter. The maximum of Q×f is achieved at 1400℃.τ_f is not influenced by sintering temperature.