|摘要: ||本研究中製備的兩系列樣品分別為R2Zr2O7 (R = La, Eu, Dy, Ho, Er, Yb)以及R2ZrTiO7 (R = Eu, Dy, Ho, Er, Yb, Lu) 複合材料。另外，製備R2Zr2O7 (R = Eu, Ho, Yb) 和R2ZrTiO7 (R = Eu, Ho, Yb) 氧化物與複合材料作比較。複合材料是在氧化物中加入1:1莫爾比混合的碳酸鋰和碳酸鈉而得。碳酸鹽以非晶相的形式存在於具有孔洞的氧化物樣品中。R2Zr2O7系列樣品中，除了La2Zr2O7及Eu2Zr2O7為焦綠石結構外，其餘皆為螢石結構。而R2ZrTiO7系列樣品則全為焦綠石結構。結構與A2B2O7中A、B兩陽離子半徑比rA/rB有直接關係，半徑比 > 1.47時 (Zr4+以6配位計算)，晶體結構為焦綠石結構；反之，則為螢石結構。隨著取代元素的離子半徑增加，晶格的軸長也隨之增加。氧化物粒子大小約為0.3 micrometer。無論是複合材料或是氧化物皆有很高的緻密性。氧化物導電度隨溫度上升而緩緩增加。複合材料導電度隨溫度上升可分為三段。低溫部分300°C~450°C導電度隨溫度上升而緩緩增加。當溫度到達接近碳酸鹽熔點的475°C~525°C時，導電度急遽增加。而550°C~700°C時碳酸鹽已完全熔融，導電度不隨溫度上升有明顯變化。不過，Yb2ZrTiO7複合材料長時間測試 (650°C，24 h)，導電度會下降且碳酸鹽會流失。複合材料在500°C時的導電度高出氧化物3~5數量級。525°C時，Er2Zr2O7複合材料有最高的導電度，達 1.440(9) × 10-1 S•cm-1。在此溫度下，所有複合材料導電度都在1.44~0.72 × 10-1 S•cm-1之間。從目前的測試結果，R2Zr2O7與R2ZrTiO7複合材料一樣好。不過，Ti的價數容易改變；而Zr的4價非常穩定， R2Zr2O7複合材料的應用價值應該超過R2ZrTiO7複合材料。建議此研究所得的複合材料若使用在固態氧化物燃料電池中作為電解質時的操作溫度是500°C。|
In this study, two series of samples were prepared, they were R2Zr2O7 (R = La, Eu, Dy, Ho, Er, Yb) and R2ZrTiO7 (R = Eu, Dy, Ho, Er, Yb, Lu) composites. In order for comparison, R2Zr2O7 (R = Eu, Ho, Yb) and R2ZrTiO7 (R = Eu, Ho, Yb) oxides were also prepared. Composites were prepared by immersing the oxides into 1:1 molar ratio of Li2CO3 and Na2CO3. Carbonates are in the amorphous form. In R2Zr2O7 series, except the La2Zr2O7 and Eu2Zr2O7, they have pyrochlore phase, the rest of the oxides have fluorite phase. In R2ZrTiO7 series, all sample have pyrochlore phase. The phases of the oxides depend on the radius ratio of rA/rB in the A2B2O7 pyrochlore structure. When the ratio is > 1.47(calculation based on the Zr4+ in 6-coordination number), materials have pyrochlore phase. In contrast, materials have fluorite phase. For the oxides, increasing the ionic radii of cations, unit cell a-axes increase. They obey Vegard’s law well. Particle size of oxides is about 0.3micrometer. Both composites and oxides are dense enough for conductivity measurements. There are three regions observed in the temperature dependent conductivity measurements on the composites. In the low temperature range from 300°C to 450°C, conductivity increases slowly with increasing temperature. In the temperatures close to the melting point of the carbonates, 475°C~525°C, conductivity increases rapidly. When the temperature reaches to 550°C~700°C, the carbonates are melted, conductivity does not varied significantly with temperature. At 500°C, conductivity of the composite is order magnitude higher than that of the oxide. For all the materials, Er2Zr2O7 composite has the highest conductivity 1.440(9) × 10-1 S•cm-1 at 525°C; all of them have conductivity between 1.44 ~ 0.723 × 10-1 S•cm-1. Nevertheless, conductivity is gradually decreasing with long time measurement (650°C, 10 h) on the sample of Yb2ZrTiO7. In this study, performance of R2ZrTiO7 composites is as good as R2Zr2O7 composites. However, valence of Ti4+ can be changed, but Zr4+ is very stable. From this point of view, R2Zr2O7 composites are better candidates as electrolytes in the solid oxide fuel cell and the operation temperature can be lowered to 500°C.