(A’1/3A”2/3)1/2Ti1/2O2 (A’:Mg, Ni, Zn; A”:Nb, Ta)微波陶瓷材料之拉曼光譜與延伸x光吸收精細結構分析
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2008
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Abstract
本文利用拉曼散射、X光繞射和延伸X光精細結構光譜（EXAFS）等光學方法來測量擁有金紅石(rutile)結構的(A’1/3A”2/3)1/2Ti1/2O2樣品（A’: Mg, Ni, Zn; A”: Nb, Ta）中氧八面體結構與其微波性質的關連性。藉由改變不同的A’及A”的原子，品質因子和介電常數都有顯著的變化。在此，我們將我們的樣品分成兩組：一組為(A’1/3Nb2/3)1/2Ti1/2O2，(A’: Mg, Ni, Zn)；另一組為(A’1/3Ta2/3)1/2Ti1/2O2，(A’: Mg, Ni, Zn)。
從EXAFS的分析可以發現：不同的A’原子，其Ti-O鍵長（即氧八面體體積）會產生不同的變化，而且散射中心到相鄰單位晶格中心的距離(即c軸長度)對於介電常數有著非常大的影響。在拉曼部份，我們比對了1倍及具有奈米結構的金紅石拉曼圖形，發現到我們的拉曼實驗數據較為接近奈米結構的金紅石，這也就是說我們的樣品具有奈米結構的特性。此外，與氧原子相關的拉曼振動模基本上會隨著A’原子的重量增加而產生紅移。透過理論的計算所得到的頻率變化趨勢，與我們分析得到的頻率變化趨勢相同，且都與介電常數有關－氧八面體結構越緊密，介電常數越小；另外透過比對與氧原子相關的拉曼振動模峰值的半高寬與品質因子，我們得到了半高寬越小品質因子越好的結果。從拉曼散射和延伸X光精細結構光譜實驗都顯示本文材料的微波特性與氧八面體微觀結構直接相關。
The conventional-grown (A’1/3A”2/3)1/2Ti1/2O2 Rutile ceramics (with A’: Mg, Ni, Zn; A”: Nb, Ta) were examined by Raman spectroscopy and extended x-ray absorption find structure (EXAFS) to correlate the microstructure with the microwave dielectric properties. The microwave dielectric properties of (A’1/3A”2/3)1/2Ti1/2O2, such as Qxf value and dielectric constant, are mainly due to the A'and A" atom substitution. The EXAFS analysis found that the Ti-O bond lengths are the crucial factor for the dielectric constant. The Ti-O bond lengths distances between scattering center and its neighboring atoms are measured, and the shorter the bond length. By comparing the Raman spectra of our samples with the ones of bulk-rutile and nanocrystallien-rutile which are report in literatures, the samples’ Raman experiment data are found closed to nanocrystallien-rutile, we can conclude these samples have nano structure characteristic. Besides, oxygen-octahedral Raman vibration phonon modes are shifted to lower frequencies with the increasing atomic weight of A’ site. The observed phonon shifts are agreed with the calculation that based on the results of EXAFS analyzing. The dielectric constant decreases with the tightening oxygen-octahedral structure. Moreover, the phonon FWHM is strongly correlated with the microwave Qxf value, which indicates the propagation of the microwave EM wave is assisted by the “closed packed” octahedron structure.
The conventional-grown (A’1/3A”2/3)1/2Ti1/2O2 Rutile ceramics (with A’: Mg, Ni, Zn; A”: Nb, Ta) were examined by Raman spectroscopy and extended x-ray absorption find structure (EXAFS) to correlate the microstructure with the microwave dielectric properties. The microwave dielectric properties of (A’1/3A”2/3)1/2Ti1/2O2, such as Qxf value and dielectric constant, are mainly due to the A'and A" atom substitution. The EXAFS analysis found that the Ti-O bond lengths are the crucial factor for the dielectric constant. The Ti-O bond lengths distances between scattering center and its neighboring atoms are measured, and the shorter the bond length. By comparing the Raman spectra of our samples with the ones of bulk-rutile and nanocrystallien-rutile which are report in literatures, the samples’ Raman experiment data are found closed to nanocrystallien-rutile, we can conclude these samples have nano structure characteristic. Besides, oxygen-octahedral Raman vibration phonon modes are shifted to lower frequencies with the increasing atomic weight of A’ site. The observed phonon shifts are agreed with the calculation that based on the results of EXAFS analyzing. The dielectric constant decreases with the tightening oxygen-octahedral structure. Moreover, the phonon FWHM is strongly correlated with the microwave Qxf value, which indicates the propagation of the microwave EM wave is assisted by the “closed packed” octahedron structure.
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金紅石, 微波陶瓷, 拉曼, 延伸X光吸收精細結構, rutile, microwave ceramic, Raman, EXAFS