本論文使用沉澱法製備不同元素摻雜之二氧化鈰奈米顆粒，並以一系列的光譜分析探討被摻雜物誘發的缺陷結構，包括X光吸收光譜、拉曼光譜、紫外/可見光吸收光譜以及掃描穿透電子顯微鏡/電子能量損失光譜等，最後結合磁性量測結果，建立缺陷與磁性之關係。探討的主題有二：缺陷結構與缺陷分布。其中缺陷結構以摻雜不同類型元素進行討論，第一部份為不同離子半徑，包括La與Y。第二為不同電子組態，包括Pr及La。缺陷分布的影響則是分析退火前後之摻雜Pr之二氧化鈰奈米顆粒。
首先在離子半徑大小不同的La與Y摻雜二氧化鈰奈米顆粒方面，其摻雜濃度從0到15 at%。從X光吸收光譜與拉曼光譜的量測分析可發現隨著摻雜量增加，氧空缺的含量也跟著上升。在低摻雜量時主要氧空缺所造成的缺陷結構為M3+-Vo¬- M3+ (M= Ce, La or Y)，而當摻雜量高於7%後，缺陷結構開始逐漸形成La3+-Vo-La3+或Y3+-Vo-Y3+。接著從掃描式穿透電子顯微鏡及電子能量損失光譜的分析發現在La摻雜二氧化鈰奈米顆粒中，La3+與Ce3+離子在系統中分布情形並不明顯，僅有少許聚集於顆粒中，而Y摻雜二氧化鈰奈米顆粒則趨向聚集於顆粒表面，造成該缺陷分布不同的原因可歸因於摻雜物離子半徑大小的不同。最後比較鐵磁性與缺陷關係發現摻雜La之二氧化鈰奈米顆粒的磁性較Y摻雜的弱，即表面的缺陷濃度高會貢獻較大的鐵磁性。
在電子組態不同的Pr摻雜二氧化鈰奈米顆粒研究方面，同樣以0到15 at%的摻雜濃度做合成。首先使用X光吸收光譜確認當Pr摻雜於系統中不論摻雜量多寡皆是以Pr3+形式存在，而Ce3+含量則隨著Pr摻雜量增加而產生改變，從開始的9%左右上升到10%後，當Pr摻雜量大於9%後Ce3+即隨之下降。此外，Pr摻雜二氧化鈰奈米顆粒從VSM的量測得知樣品皆為室溫鐵磁性。綜合拉曼光譜、X光吸收光譜與磁性結果比較，可發現缺陷結構會依Pr摻雜量增加而改變，接著使用FCE機制可推論出二氧化鈰奈米顆粒中缺陷結構與磁性關係的影響，並比較La摻雜二氧化鈰奈米顆粒探討電子組態與磁性的影響。
繼續將Pr摻雜二氧化鈰奈米顆粒在氧氣氣氛下做退火處理，使用X光吸收光譜中的Pr L-edge可清楚得知，經過氧氣退火後Pr依舊以三價的形式存在系統中沒有被氧化。而Ce3+含量則比退火前減少了許多，從8-10%下降到7-8%。拉曼光譜的分析也發現高摻雜量時缺陷結構從退火前的Pr3+-VO-Ce3+變成Pr3+-VO-Pr3+。從掃描式穿透電子顯微鏡及電子能量損失光譜發現，退火後系統中的Ce3+會聚集於顆粒表面，缺陷分布與磁性的關係將由FCE機制來建立。最後，本實驗討論因氧空缺產生的未束縛電子分布，更完整的詮釋有效F+ center在二氧化鈰奈米顆粒中影響鐵磁性的濃度。

In this study, the relationship between the defect structure and magnetism of doped CeO2 nanoparticle (NPs) was prepared by precipitation method, and was systematically investigated by using spectroscopy and microscopy. Including X-ray absorption spectroscopy (XAS) and Raman spectroscopy were utilized to investigate the electronic structure of these doped CeO2 NPs.
First, different size of ionic radius dopant, La and Y were doped in CeO2. It was found that the content of oxygen vacancies increased upon increasing dopant. The major oxygen vacancy defect structure was M3+−VO−M3+ (M = Ce, La or Y) in lightly doped NPs, whereas it changed to La3+−VO−La3+ or Y3+-Vo-Y3+ as the doping level reached 7%. Scanning transmission electron microscopy coupled with electron energy loss spectroscopy (STEM/EELS) analysis showed that, in the La-doped NPs, both the dopant (La3+) and Ce3+ were distributed rather homogeneously within the NPs, which is different from the behavior in other doped ceria materials, whereas Y-doped CeO2, for which strong interactions among the surface, trivalent cerium, and dopant. The distinct distribution of defects was attributed to the larger ion radius of La and the nature of the La-related oxygen vacancies. Moreover, room-temperature ferromagnetism (FM) was observed in these La-doped ceria but with a weaker intensity compared to the magnetism obtained for other doped ceria NPs with similar dopant concentrations. This indicates that high concentrations of defects and dopant at the surface are critical for obtaining larger FM.
Next, Pr3+(4f2) has different electron configuration from La3+(4f0), it is demonstrated that by raising the content of Pr, the degree of oxygen deficiency is enhanced monotonically, suggesting that oxygen and/or oxygen-related vacancies are induced. XAS analysis indicates the preference of the Pr-ions for the Pr3+ oxidation state. The concentration of Ce3+ stay constant at 9% then raise to 10% when Pr reaches 9%, with further Pr doping, Ce3+ decreases to 8%. From the results of Raman spectroscopy, the defect structures evolved from Ce4+-VO-Ce3+ to Pr3+-VO-Ce3+ as Pr contents increase. Together all spectroscopic results, the structure and evolution of above oxygen related defect was then unraveled. Furthermore, all the Pr-doped CeO2 NPs were found to be ferromagnetic at room temperature. The relationship between defect structure and ferromagnetism is explained by FCE mechanism.
Then Pr-doped CeO2 NPs were annealed in O2 atmosphere. From the results of spectroscopy, the defect structures become Pr3+-VO-Pr3+ in high doping level of O2 annealed Pr-doped CeO2 NPs while Ce4+-VO-Ce3+, Pr3+-VO-Ce3+ in Pr-doped CeO2. It is also observed that the distribution of oxygen vacancies after samples annealed is inhomogeneous from microscopy, although the ratio of Ce3+ slightly decreases after annealing, Ce3+ ions aggregate at the surface of particles. The relationship between defect structure and ferromagnetism can be explained by FCE mechanism. Furthermore, the amount of F+ center can be estimated by the results of XANES Ce L-edge and Raman spectroscopy. It is found the saturated magnetization is strongly related to the amount of F+ center in doped CeO2 NPs.

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