本實驗利用固態合成法來製備所有陶瓷樣品，將Mg4Nb2O9摻雜TiO2或SrTiO3，並研究樣品結構和微波介電特性。在實驗過程中，使用過量莫耳比的MgO能將反應物穩定在Mg4Nb2O9相，但未參與反應的MgO會使介電特性下降。
添加TiO2會使Mg4Nb2O9形成二次相Mg5Nb4O15，由於TiO2會熔於Mg4Nb2O9並取代Nb離子，二次相會隨TiO2添加量增加而增加；由SEM分析觀察到添加TiO2能降低燒結溫度，提高晶粒生長，隨燒結溫度升高，有異常晶粒生長的現象；由Raman光譜分析能明顯觀察添加TiO2對於Mg5Nb4O15相與Mg4Nb2O9相震動模式的變化。
添加SrTiO3會使Mg4Nb2O9分解，並Mg4Nb2O9的Nb離子溶解到SrTiO3中，取替Ti離子位點並形成SryNbO3結構，以及過多的MgO變成二次相；從 Raman光譜分析並沒有觀察到SryNbO3的震動模式。
添加TiO2會引起相變，Q×f值隨著TiO2的增加而迅速下降，介電常數也隨著TiO2增加而降低；添加SrTiO3會使Q×f值隨著添加量的增加而降低，但介電常數隨 SrTiO3增加而增加。樣品能增加燒結溫度減少孔隙率並提高緻密度能提高微波介電性能。
In this study, we are synthesized the Mg4Nb2O9 ceramics by the mixed oxide method and added to TiO2 or SrTiO3 in order to study the microstructure and microwave properties of this mixture. The over-stoichiometry MgO reactant can steady the Mg4Nb2O9 phase during the synthesized processing, but the residual MgO reactant also can influence microwave property.
The Mg4Nb2O9 ceramics can transform into Mg5Nb4O15 phase due to additive TiO2. The Mg5Nb4O15 phase of the samples is increasing with TiO2 additive increasing, which is due to TiO2 dissolving into ceramic and replacing Nb-ion site. The microstructure of samples is shown that TiO2 additive can reduce the sintering temperature, improve the grain growth and increase more Mg5Nb4O15 phase. The SEM images are observed the equiaxed Mg4Nb2O9 grains and columnar Mg5Nb4O15 grains, and the samples are showed the abnormal grain growth (AGG) phenomenon with sintering temperature increasing. The room temperatures Raman spectrum of samples are observed the Mg4Nb2O9 and Mg5Nb4O15 phonon modes, which is also shown the same phase transformation during TiO2 additive increasing.
The Mg4Nb2O9 ceramics can be decompose by additive SrTiO3, because the Nb-ion of Mg4Nb2O9 ceramics can be dissolving into SrTiO3, replacing Ti-ion site and formed SryNbO3 structure: then the excess MgO become second phase. The SEM images are observed the larger Mg4Nb2O9 grains and smaller SryNbO3 grains, and the samples are showed the grain growth with sintering temperature increasing. The room temperatures Raman spectrum of samples are only observed the Mg4Nb2O9 phonon modes without SryNbO3.
Because the TiO2 additive can be inducing the phase transformation, the Qxf -values of mixture is rapidly decreasing with TiO2 increasing: but the K-values of samples are small fluctuation with TiO2 additive increasing. The Qxf -values of SrTiO3 mixture is also decreasing with additive increasing: but the K-values of samples are larger increasing with high-K SrTiO3 additive increasing. The microwave dielectric property can be enhanced by increasing sintering due to low porosity.
