| 研究生: |
李品賢 Li, Pin-Hsien |
|---|---|
| 論文名稱: |
正方鎢青銅結構之化合物:K2EuxFe1-x+δNb5-0.6δO15的合成及其磁電特性 Synthesis of tetragonal-tungsten-bronze type compound:K2EuxFe1-x+δNb5-0.6δO15 and characterisation of their electrical and magnetic properties |
| 指導教授: |
齊孝定
Qi, Xiaoding |
| 學位類別: |
碩士 Master |
| 系所名稱: |
工學院 - 材料科學及工程學系 Department of Materials Science and Engineering |
| 論文出版年: | 2009 |
| 畢業學年度: | 97 |
| 語文別: | 中文 |
| 論文頁數: | 87 |
| 中文關鍵詞: | 固相燒結法 、正方鎢青銅結構 |
| 外文關鍵詞: | TTB structure, solid state sintering |
| 相關次數: | 點閱:78 下載:1 |
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目前已知許多正方鎢青銅結構(Tetragonal Tungsten Bronze,TTB)的化合物為鐵電材料,其典型代表如Ba2NaNb5O15。本實驗希望在保有鐵電特性的結構下,加入稀土或是過渡金屬元素,可以改變磁特性。
本實驗利用固相燒結法及溶膠凝膠法,期望能將合成K2EuxFe1-x+δNb5-0.6δO15的化合物,並藉由調整Eu和Fe在此化合物中的比例,觀察此化合物在結構及其他性質上面的變化。
實驗結果可以發現:利用固相燒結法,K2EuxFe1-x+δNb5-0.6δO15在950℃12小時可以生成TTB結構,但同時也包含些許雜相,尤以Fe2O3(Hematite,赤鐵礦)最為常見。為了去除Fe2O3,可以使用鹽酸去反覆洗滌粉體,可以發現HCl除了可以溶解並去除大部分的Fe2O3之外,不會產生新的化合物,也不會破壞TTB結構。由於Fe跟Eu離子大小的差異,使得可以填入TTB結構中的位置也不同;因此若是對照XRD圖形,改變Eu和Fe的比例,也會改變TTB結構的種類。從EDS可以發現:進入TTB結構Fe數量,並不如預期的多,這應是雜相Fe2O3容易形成的原因之一。
磁性方面:在未使用HCl清洗以前,從M-T曲線可以發現:在250K附近,會出現臺階狀的圖形。但經由HCl清洗去除部分雜相後,臺階狀的磁性特性便消失,幾可確認此一磁性現象是由Fe2O3的Morin transition而來,而非由TTB結構所提供。而K2EuxFe1-x+δNb5-0.6δO15成分下形成的TTB結構可能為亞鐵磁性。
電性方面:雖然可以利用膠體懸浮法製成薄膜,但存在漏電流的問題。經固相燒結法及HCl清洗後,雖然仍可以看見漏電流的情形,但在較低的電壓下,可以出現極化的趨勢。
There are many compounds of TTB structure shows ferroelecricity, such as Ba2NaNb5O15. Our approach here to change the magnetic property by adding rare earth or trasition metal element, and keep the TTB structure intact.
The focus of research is to synthesize the compound,K2EuxFe1-x+δNb5-0.6δO15 and modulated the ratio between Eu and Fe by solid state sintering as well as sol-gel. Various characterization techniques were empolyed to find the structural changes and its fundamental properties.
The experimental results showed that TTB structure could be prepared at 950 oC in air for 12hr by solid state sintering, but had other compounds at the same time, like Fe2O3. In order to remove Fe2O3, we used hydrochloric acid to wash the powder repeatedly. We find that hydrochloric acid could selectively remove the iron oxide. Hydrochloric acid did not form any new compound, nor did it not destroy the TTB structure. When the Eu to Fe ratio changed, the types of TTB structure also changed as observed from XRD analysis. The number of Fe ion entered the TTB structure is not as good as Eu ion, and we could observer that from the EDS data.
Before the removal of impure phases by hydrochloric acid, the M-T curive contained a step near to 250K. After using hydrochloric acid, the step got disappeared. Compared to every feasible impure phase, we thought the step from the Morin transition is because of Fe2O3. The TTB structure is ferrimagnetic when the nominal composition is K2Eu0.8Fe1.2Nb4.4O15.
Here we also prepared the film by colloidal suspensions method, but observed a large leakage current. Hydrochloric acid was used to avoid impure phases in bulk. Although the problem about leakage current still occurred, but we could observe the trend of polarization by electric field.
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