鎵石榴石微波陶瓷的延伸X光吸收精細結構與拉曼光譜研究

Abstract

本文以延伸x光精細結構光譜(Extended X-ray absorption fine structure)與拉曼散射光譜(Raman spectrum)對Re3Ga5O12 Gallium Garnet陶瓷的微波特性相關性質進行研究，其中A-site元素由不同的稀土族元素所置換，分別為Nd, Sm, Eu, Dy，在X光精細結構光譜的研究中，可發現鎵多面體的相對大小與晶體的介電常數(Dielectric constant)有關；而由對拉曼光譜的分析，可歸納出聲子的半高寬與品質因子（Quality factor）間的關連性，當聲子半高寬較小時，表示晶體的結晶性良好，晶體的振動因而能與外加電磁波的頻率一致（coherent）。關連不同原子結構的聲子性質亦被分析，與A-site結構相關的聲子頻率較高時，表示A-site氧十二面體的體積較小，而鎵多面體的相對體積較大，介電性質的變化被發現與多面體間的相對體積變化有關。 在摻雜TiO2共同燒結的Sm-Garnet微波特性研究中，我們同樣利用EXAFS與拉曼光譜進行分析，結果顯示，Garnet結構並沒有顯著的改變，而在晶粒的邊界中存在有Ga2O3以及鈦原子相關的化合物，這些二次相的出現降低了邊界的電磁波反射，改善了微波特性。Gallium Garnet ( Re3Ga5O12 , Re = Nd, Sm, Eu, Dy ) has potential to be a new candidate material for MIC application. We perform EXAFS and Raman experiments to investigate the lattice structure under different atomic composition. The correlation between dielectric constant and relative volume of gallium centered polyhedron is studied through EXAFS. The dielectric constant increases with the increasing relative volume of Gallium centered polyhedron. Raman spectroscopy reveals that the FWHM of phonons are strong correlated to the quality factor. The Raman shift of the A-site corresponding phonon moves to higher frequency as the dielectric constant increasing, which is agreed with the observation in EXAFS. The gallium rich phase Ga2O3 and some titanium compound are found to be between the boundaries of grains of the Sm-Garnet with 1mol% TiO2 added. It is believed these non-garnet phases play the roles that efficiently lower the reflectance of the EM wave when crossing the boundaries and result in higher quality factor.