La(2-x)/3NaxTiO3與Nd(2-x)/3LixTiO3微波陶瓷材料之拉曼光譜與延伸X光吸收精細結構
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2008
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本文將討論A2/3BO3缺陷型鈣鈦礦材料，利用拉曼散射及延伸X光吸收精細結構 (EXAFS) 的量測，得到摻雜鈉的La(2-x)/3NaxTiO3 (0.02≦x≦0.5) 與摻雜鋰的Nd(2-x)/3LixTiO3 (0.1≦x≦0.5) 之結構與微波介電特性的關聯性。從X光繞射與拉曼光譜中，兩種材料在光譜上皆有明顯改變，估計有相變發生。從群論理論分析，可得到拉曼光譜中各頻率代表的原子振動方式。拉曼光譜在200~400 cm-1區域中，與A-site相關的E (239、254 cm-1) 與A1 (322、338 cm-1) 振動模，隨著摻雜鈉與鋰的濃度增加，La(2-x)/3NaxTiO3與Nd(2-x)/3LixTiO3分別表現出紅移與藍移的現象，聲子頻率位移相反與A-site縮減質量速度和介電常數上升快慢有關聯。拉曼光譜得到AO12 (AO6) 的緊密度變大，會使得B-site的鍵結強度減弱。Nd(2-x)/3LixTiO3中的A1 (471 cm-1) 振動膜發現有紅移現象，表示沿z軸上O-Ti-O鍵結強度變鬆散。由EXAFS得知，Nd(2-x)/3LixTiO3在x≦0.3時，隨著摻雜鋰的濃度愈高，平均Ti-O的鍵長增加，即氧八面體變大與介電常數成正比，且沿著z軸上O-Ti-O的鍵長也增加；x>0.3時，隨鋰摻雜增加，平均Ti-O鍵長縮小，亦與介電常數成正比。隨著摻雜物增加，A-site有序性減小，拉曼光譜中的各聲子半高寬均變寬，與Q×f值成反比。由拉曼散射與X光吸收精細結構實驗中，皆可得到兩系列材料的微波介電特性，與內部微結構均有密切的關係。
A-site deficient perovskite compounds found in La(2-x)/3NaxTiO3 (0.02≦x≦0.5) and Nd(2-x)/3LixTiO3 (0.1≦x≦0.5) microwave ceramics were investigated by Raman scattering and extended X-ray absorption fine structure (EXAFS) measurement at room temperature to reveal the correlation between microwave dielectric properties and micro-structure. From the lineshape of X-ray diffraction and Raman spectra, phase transitions were found. Group theoretical analysis of Raman active modes de-cided vibrations of phonons in Raman spectra. During 200 to 300 cm-1 frequency re-gion, E (239, 254 cm-1) and A1 (322, 338 cm-1) modes shifted in the opposite way are due to the decreasing rate of reduced mass and the increasing speed of dielectric con-stant. Therefore, the increase of A-site bonding strength weakens the B-site bonding force. The 471 cm-1 peak (A1 symmetry) redshift with the lithium concentration, this result indicated O-Ti-O bonding force decreases along the z-axis. EXAFS results of Nd(2-x)/3LixTiO3 obtained, when x≦0.3, the average Ti-O bond length of the first shell and O-Ti-O bond length increase, as expected the results that bonding force decrease with the lithium concentration from the analysis of E (239, 254 cm-1), A1 (322, 338 cm-1), and A1 (471 cm-1) peaks; when x>0.3, the Ti-O bond length decrease with the lithium concentration. The volume of TiO6 is proportional to dielectric constant. Wider widths of phonons caused by the A-site disordering imply the decrease of Q×f value. The microwave dielectric properties and micro-structure have reciprocal relationship as discussed above.
A-site deficient perovskite compounds found in La(2-x)/3NaxTiO3 (0.02≦x≦0.5) and Nd(2-x)/3LixTiO3 (0.1≦x≦0.5) microwave ceramics were investigated by Raman scattering and extended X-ray absorption fine structure (EXAFS) measurement at room temperature to reveal the correlation between microwave dielectric properties and micro-structure. From the lineshape of X-ray diffraction and Raman spectra, phase transitions were found. Group theoretical analysis of Raman active modes de-cided vibrations of phonons in Raman spectra. During 200 to 300 cm-1 frequency re-gion, E (239, 254 cm-1) and A1 (322, 338 cm-1) modes shifted in the opposite way are due to the decreasing rate of reduced mass and the increasing speed of dielectric con-stant. Therefore, the increase of A-site bonding strength weakens the B-site bonding force. The 471 cm-1 peak (A1 symmetry) redshift with the lithium concentration, this result indicated O-Ti-O bonding force decreases along the z-axis. EXAFS results of Nd(2-x)/3LixTiO3 obtained, when x≦0.3, the average Ti-O bond length of the first shell and O-Ti-O bond length increase, as expected the results that bonding force decrease with the lithium concentration from the analysis of E (239, 254 cm-1), A1 (322, 338 cm-1), and A1 (471 cm-1) peaks; when x>0.3, the Ti-O bond length decrease with the lithium concentration. The volume of TiO6 is proportional to dielectric constant. Wider widths of phonons caused by the A-site disordering imply the decrease of Q×f value. The microwave dielectric properties and micro-structure have reciprocal relationship as discussed above.
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鑭鈉鈦氧, 釹鋰鈦氧, A位置空缺, 拉曼, La(2-x)/3NaxTiO3, Nd(2-x)/3LixTiO3, A-site vacancy, Raman