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| 題名: | BaZrO3, LaAlO3, R2(Zr,Ti)2O7 (R = La, Dy, Er)氧化物及其與(LiNa)2CO3複合材料的離子導電度研究 |
| 其他題名: | Ionic conductivity of BaZrO3, LaAlO3, R2(Zr,Ti)2O7 (R = La, Dy, Er) oxides and their (Li/Na)2CO3 composite materials |
| 作者: | 解佳穎;Hsieh, Chia-Ying |
| 貢獻者: | 淡江大學化學學系碩士班
高惠春 |
| 關鍵詞: | 離子導電;鈣鈦礦;焦綠石;螢石;固態電解質;固體氧化物燃料電池;複合材料;ionic conductivity;perovskite;pyrochlore;fluorite;solid state electrolyte;solid oxide fuel cell;Composite material |
| 日期: | 2012 |
| 上傳時間: | 2013-04-13 11:04:10 (UTC+8) |
| 摘要: | 本研究中製備的樣品分別為 BaZrO3、LaAlO3、R2Zr2O7 (R = La、Dy、Er) 以及 R2(ZrTi)O7 (R = La、Dy、Er) 的氧化物及其複合材料。BaZrO3和LaAlO3為鈦酸鈣礦結構；La2Zr2O7、R2(ZrTi)O7為焦綠石結構；Dy2Zr2O7 和 Er2Zr2O7 為螢石結構。焦綠石部分皆為無序，R離子半徑增加，8b位置上的O(3) 佔有率下降，O(1) 位置的 x 座標增加。複合材料中(Li/Na)2CO3熔點溫度為495oC，分解溫度為519oC。利用490oC測量Eu2Zr2O7複合材料11天後導電度趨於穩定約為5.6 × 10–2 S‧cm–1 ± 4.6 %。複合材料在500oC的導電度比氧化物高出約4-5個數量級；並且複合材料在500oC時的導電度大約都在10-1 S‧cm-1。本研究中BaZrO3、LaAlO3、R2(Zr,Ti)O7中最佳導電度的La2Zr2O7以及Dy2(ZrTi)O7純氧化物在700oC導電度分別為4.55 × 10-7、6.7 × 10-8、3.41 × 10-4以及5.23 × 10-4 S‧cm-1。R2(Zr,Ti)O7氧化物的導電度主要受到R離子半徑的傳導距離和陽離子束縛力影響，與螢石和焦綠石結構間的變化較無明顯的關聯性。氧化物的活化能約在0.42–1.42 eV之間，主要是受a-軸的影響；隨著a-軸增加而下降，在相同的R之下R2Zr2O7比R2(ZrTi)O7樣品高。複合材料的導電度分為兩個明顯的區段，分別為(Li/Na)2CO3熔點前後，熔點前導電度較純氧化物高出2-3個數量級；熔點後因活化能降至0.05-0.21 eV之間，此時的導電度高於純氧化物4-5個數量級，導電度約為 10-1 S‧cm-1左右。R2(ZrTi)O7系列的樣品Ti元素的混價會使得該系列樣品隨著測量溫度的上升，電子導電所佔的比例也跟著增加，由吸收光譜得知Ti元素的價數約為3.4價。除了R2(ZrTi)O7高溫下會有變價現象外，R2Zr2O7和500oC下的R2(ZrTi)O7製作成複合材料後適合當作電解質使用。
In this study, dense oxides and their composites of BaZrO3, LaAlO3, R2Zr2O7 (R = La、Dy、Er) and R2(ZrTi)O7 (R = La、Dy、Er) were prepared. Carbonate composites were prepared into 1:1 molar ratio of Li2CO3 and Na2CO3. The BaZrO3 and LaAlO3 have perovskite structure; La2Zr2O7 and all of R2(ZrTi)O7 are pyrochlore phase, Dy2Zr2O7 and Er2Zr2O7 are fluorite. All the pyrochlore phase materials are disorder. Occupancy of the O(3) sites decreases with increasing the radii of the R cations; In addition, x-coordinates of the O(1) site increase. Melting point and decomposing point of (Li/Na)2CO3 are 495oC and 519oC, respectively. At 490oC, after 11 day, conductivity of the Eu2Zr2O7–composite is 5.6 × 10–2 S‧cm–1 ± 4.6 % and levels off. Electrical conductivity of BaZrO3, LaAlO3, La2Zr2O7 and Dy2(ZrTi)O7 are 4.55 × 10-7, 6.7 × 10-8, 3.41 × 10-4 and 5.23 × 10-4 S‧cm-1 in 700oC, respectively. Conductivity of all the zirconate composites is in the order of 10-1 S‧cm-1 and it is 3 to 5 orders of magnitude larger than that of the oxides at 500oC. Conductivity of the zirconates is governed by the oxygen ion transport distances and the bonding strength between the R cation and oxygen atoms. It seems not related to the fluorite to pyrochlore phase transformation. Activation energy (Ea) of the zirconates decreases with increasing the unit cell a-axis. They are between 0.52 – 1.42 eV. For the same R, Ea of the R2Zr2O7 is higher than that of the R2(ZrTi)O7. At temperature lower than the melting point of the (Li/Na)2CO3, conductivity of the composites higher than the oxides for about 2 to 3 orders and activation energy decreases to 0.05 to 0.21 eV. At higher temperature, all the composites have conductivity in the order of 10-1 S‧cm-1. Ionic transference numbers (ti) of the R2(ZrTi)O7 is 100%. Nevertheless, for the R2(ZrTi)O7 series, ti is 100%, 90–91% and 81–83% at 500oC, 600oC and 700oC, respectively. Ti atoms are in the mixed-valence state with a valence of 3.4+. Increasing temperature, electronic conduction increases. All of the composites studied in this research are potential electrolytes for using in the SOFC at temperatures slightly lower than 500 oC. |
| 顯示於類別: | [化學學系暨研究所] 學位論文
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