R2(Zr,Ti)2O7 (R = Y、Gd、Sm、Nd) 氧化物及其與 (Li/Na)2CO3 複合材料之導電度研究

Ionic conductivity of R2(Zr,Ti)2O7 (R = Y、Gd、Sm、Nd) oxides and their (Li/Na)2CO3 composite materials.

李阮鴻(Ruan-Hong Li)

指導教授 ： 高惠春

淡江大學/理學院/化學學系碩士班/碩士(2012年)

https://doi.org/10.6846/TKU.2012.00992

摘要

本研究中製備的兩系列樣品分別為R2Zr2O7 (R = Y、Gd、Sm、Nd)以及R2(ZrTi)O7 (R = Y、Gd、Sm、Nd) 的氧化物及其碳酸鹽複合材料。緻密的氧化物R2Zr2O7和R2(ZrTi)O7分別以1600oC及1500oC燒結。緻密的複合材料是在氧化物中加入1:1莫爾比混和的碳酸鋰和碳酸鈉而得。兩系列樣品中，當陽離子半徑比(rR/r(Zr,; Ti), Zr4+及Ti4+以6配位計算) ≥ 1.48時，晶體結構為pyrochlore；反之，為fluorite。R2Zr2O7及R2(ZrTi)O7氧化物的導電度分別約在10–4 S•cm–1和10–5 S•cm–1；受到R離子半徑的影響較大，與fluorite和pyrochlore結構間的變化較無明顯關係。氧化物的活化能，約在0.52–1.30 eV之間，隨著a-軸增加而下降；且在相同的R之下，R2Zr2O7的活化能比R2(ZrTi)O7高，約在0.52–1.30 eV之間。複合材料的導電度，在低於碳酸鹽熔點495oC時，導電度比氧化物高出約2–3個數量級。高於熔點時，活化能較低，約在0.05– 0.21 eV之間，導電度大約都在10–1 S•cm–1左右。R2Zr2O7系列樣品的離子遷移率在500–700oC時都很接近100%。R2(ZrTi)O7系列的樣品在500oC、 600oC、700oC時的遷移率分別約在100%、90–91%、81–83%之間。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，Ti元素的價數約為3.4價。Dy2(ZrTi)O7複合材料在490oC下，經過11天之後導電度趨於穩定約為4.65(5) x 10–2 S•cm–1。兩系列樣品製成複合材料後皆適合在接近500oC時作為固態氧化物燃料電池的電解質使用。

關鍵字

離子導電 ； 焦綠石 ； 螢石 ； 固態電解質 ； 固態燃料電池 ； 複合材料

並列摘要

In this study, two series of oxides and their carbonate composites with formula as R2(Zr,Ti)2O7 (R = Y, Gd, Sm, Nd) were prepared. Dense R2Zr2O7 and R2(ZrTi)O7 oxides were sintered at 1600oC and 1500oC, respectively. Dense composites were prepared by immersing porous oxides into 1:1 molar ratio of Li2CO3 and Na2CO3. When cation radius ratio (rR/r(Zr,Ti), 6-coordination number used for the Zr4+ and Ti4+ ions) is ≥ 1.48, samples have pyrochlore phase; on the other hand, they have fluorite phase. Electrical conductivities of the R2Zr2O7 and R2(ZrTi)O7 are in the reange of 10–4 and 10–5 S•cm–1, respectively that is related to the radius of the R cation and no apparent relation with the pyrochlore and fluorite phase transformation is observed. Activation energy (Ea) of these oxides is in the range of 0.52–1.30 eV that decreases with increasing of the unit cell a-axis. For the same R cation, Ea of the R2Zr2O is higher than that of the R2(ZrTi)O7. For the composites, at temperature lower than the melting point of the carbonates, 495oC, conductivity is higher than that of the oxides for about 2–3 orders. On the other hand, at higher temperatures, conductivity closes to 10–1 S•cm–1 with Ea in the range of 0.05–0.21eV. 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. At 490oC, after 11 d, conductivity of the Dy2(ZrTi)O7–composite is 4.65(5) x 10–2 S•cm–1 and levels off. All of the composites studied in this research are potential electrolytes for using in the SOFC at temperatures slightly lower than 500 oC.

並列關鍵字

Ionic conductivity ； pyrochlore ； fluorite ； Solid state electrolyte ； Solid oxide fuel cell ； Composite material

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