本實驗藉由固態燒結法及射頻磁控濺鍍兩種製程製備摻鈷鐵酸鉍樣品。其中固態燒結以氧化物粉末混合，再經過燒結，製備塊材樣品。已知在固態燒結製程中鐵酸鉍相的生成容易伴隨其他雜相如 Bi2Fe4O9和 Bi25FeO40 的生成，所以藉由調整燒結參數，去得到儘可能純的鐵酸鉍相，最後再用酸洗去除殘留的雜相。隨著鈷摻雜濃度的提高，雜相 Bi2Fe4O9 的比例反而會相對降低。另一方面以氧化物粉末混合，製做射頻磁控濺鍍的靶材，控制其濺鍍條件，使其在鍍有白金的矽基板和導電玻璃 FTO 上成相，可獲得沒有雜相的鐵酸鉍薄膜。
　　藉由分光光譜儀測量薄膜樣品的吸收光譜，經由換算後，推測摻鈷鐵酸鉍的能隙為 2.79 eV，與純鐵酸鉍的理論值幾乎相同。藉由光致發光量測的發光光譜, 在 380-489nm波長之間可觀察到若干發光峰， 其中450nm為導帶到價帶之躍遷, 469nm為 Bi2+能階到價帶之躍遷， 其他發光峰之起源尚未明確。在電性質量測方面，藉由電阻對溫度變化的測量，可觀察到鐵酸鉍的電阻有隨溫度上昇而下降的現象，且電阻的變化藉由公式計算後可知，摻鈷的鐵酸鉍至少具有兩個不同的活化能，可能和鐵酸鉍內部缺陷或摻雜離子形成的能階有關，但這兩個能階似乎與光致發光光譜上觀察到的未知躍遷無關。在磁性量測方面，藉由震動樣品磁力計測量摻鈷鐵酸鉍樣品的M -H曲線，可知隨著鈷摻雜量的增加，飽和磁化量 (Ms) 和矯頑磁力 (Hc) 都有增加的趨勢。磁場下的熱重分析顯示樣品的磁化量在400 ℃時既已消失，不可能來源於磁性雜相如 CoFe2O4 (TC=520 ℃)，Fe3O4 (Tc= 585 ℃) 和 -Fe2O3 (Tc=590 ℃) 等。其磁化量的增強可能與Co離子摻雜對鐵酸鉍自旋排列的影響有關。

　　Cobalt doped bismuth ferrite were synthesized by both solid state reaction and RF magnetron sputtering. In the solid state sintering process, the formation of BiFeO3 phase was often accompanied by the appearance of some secondary phases like Bi2Fe4O9 and Bi25FeO40. To avoid the problem, various sintering conditions were tried in order to get the most pure phase possible and then, the remaining trace of any secondary phase was washed away using some acid solution. It was found that the relative amount of the secondary phase, Bi2Fe4O9, was reduced by the Co doping. Similar sintering process was used to make the Co doped BiFeO3 targets for the RF magnetron sputtering of thin film samples. Under the optimum growth parameters, the films of pure BiFeO3 phase could be grown on the Pt coated silicon and the conductive FTO glass substrates, without the presence of any secondary phase.
　　The absorption spectra of Co-doped BiFeO3 films were measured by the UV-Vis spectrometry, from which the band gap was calculated to be 2.79 eV, almost exactly the same as the theoretical value for the un-doped pure BiFeO3. Photoluminescence spectra were also measured and a number of broad emission peaks were observed over the wavelength range 380-489 nm, among which the 450 nm emission came from the inter-band transition and the 469 nm emission was probably due to the transition from the Bi2+ defect level to the valence band. The origin of other emissions is not clear yet. In the electric conduction measurements, the resistivity of the BiFeO3 samples was found to decrease with the increasing temperature. The Arrhenius plots of conductivity vs. temperature showed that there existed at least two activation energies, arising from the defect or dopant energy levels inside the band gap. However, these two energy levels seemed not to be relevant to the unknown emissions observed in the photoemission spectra. In the magnetic measurements, the vibration sample magnetometry was employed to measure the M-H curves, which showed that both the saturation magnetization and the coercivity increased with the Co doping level. Thermal gravity analysis under applied magnetic field showed that the magnetization of the Co doped samples disappeared at 400 C, manifesting that it could not possibly come from the magnetic secondary phases such as CoFe2O4 (TC= 520 C), Fe3O4 (Tc= 585 C) and -Fe2O3 (Tc= 590 C). It was more likely that the Co doping somehow modified the spin arrangements in BiFeO3.

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