本研究主要針對以高介電質(high-k material)材料為主體的稀磁性氧化物(DMOs, diluted magnetic oxides)系統，研究其生成條件和摻雜物與結晶的形狀的關連，並研究結晶大小和磁性的關係。透過溶液加熱法(solvent thermal)於化學液相環境中(chemical bath)中合成微米等級氫氧化釔奈米管(nanotube)，並嘗試調控反應溫度，以改變奈米管的外觀形狀，另一方面掺雜過渡金屬鈷和稀土元素銪，來了解氫氧化釔奈米管的成長機制；在通過氧氣氣氛退火方式，轉變為氧化釔粉末量測磁性特性。
透過X光粉末繞射分析，確認粉末樣品主體為氫氧化釔六角(hexagonal)晶型，經過氣氛退火後為氧化釔方錳鐵礦(cubic bixbyite)晶型，並且確認沒有可量測到的鈷和銪氧化物的相。再透過場發射掃描式電子顯微鏡(FE-SEM)，觀察氫氧化釔奈米管的外觀形狀和晶體大小。使用近邊X光精密吸收結構(XANES)排除摻雜原子形成氧化物或叢聚(cluster)的可能性，並以延伸X光精密吸收結構(EXAFS)分析確認鈷原子鑲嵌(interstitial)於氫氧化釔或是氧化釔的主體結構中，而銪原子鑲嵌於氫氧化釔的顆粒邊界(grain boundary)上，以此說明掺雜鈷原子的氫氧化釔結晶形狀不同於摻雜銪原子的結晶形狀。利用超導量子干涉儀(SQUID)量測掺雜鈷的氧化釔奈米管和奈米粒子，掺雜鈷的奈米管呈現反磁性(diamagnetism)，而奈米粒子則為順磁與鐵磁的混合態。
由磁性的結果我們可以推斷出當結晶大小大於一個微米時，DMO系統產生磁性的機構會被破壞。

In this thesis, we have studied the correlation between dopant element and morphology of nanotubes in yttrium hydroxide. Yttrium hydroxide nanotubes, doped with cobalt or europium, were synthesized by solvent thermal method of yttrium chloride, cobalt chloride, and europium chloride. We demonstrate that the morphology of yttrium hydroxide nanotubes can be controlled by changing the dopant material and reaction temperature. The crystal structures of yttrium hydroxide host were probed by x-ray diffraction (XRD). We confirmed the host structure is in hexagonal phase. The sizes and morphologies of nanotubes were determined by field emission scanning electron microscopy (FE-SEM). Cobalt K-edge x-ray absorption near-edge structure (XANES) spectra were used to confirm that the dopant atoms do not form oxides or cluster. Extended x-ray absorption fine structure (EXAFS) technique has been employed to probe the local environments surrounding cobalt and europium in these materials. The cobalt impurity atoms were found to locate on interstitial sites. On the other hand, the europium impurity atoms were found to locate on the grain boundary of the yttrium hydroxide nanotubes. And the difference between the positions of cobalt atoms and those of europium atoms may explain why the morphologies of cobalt doped nanotubes and europium doped nanotubes are so different. The SQUID measurement at 300K reveals that the yttrium oxide nanotubes were diamagnetic. However, the nanoparticle samples, synthesized by a similar procedure, exhibit a combination of ferromagnetism and paramagnetism. That may set an upper limit of particle size in the ferromagnetic phase to insulator phase transition in DMOs system.

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