| Summary: | 碩士 === 中國文化大學 === 化學工程與材料工程學系奈米材料碩士班 === 105 === 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.
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