The effect of aliovalent dopants on crystal structure and electrical conductivity of 8YSZ ionic conductor and SrTiO3 semiconductor

Autor: Yueh-Hsun Lee, 李岳勳
Rok vydání: 2001
Druh dokumentu: 學位論文 ; thesis
Popis: 89
Conducting oxides are important electrode materials for solid state electrochemical applications. The addition of aliovalent dopants has been recognized as an ideal method to enhance electrical properties of conducting oxides. The objective of this work was to study the effect of aliovalent dopant on the structure and conductivity for ionic conductor and SrTiO3 semiconductor. The results of this work shows that the way of charge compensation for aliovalent dopants is significantly affected by the defects structure and electrical properties of the matrix materials. For Nb2O5-doped 8YSZ, the effective charge of NbZr‧ was clearly compensated by the elimination or filling of oxygen vacancies. With the addition of Nb2O5 into 8YSZ, the destabilization was observed. For 10 mol% Nb2O5 doped 8YSZ, the cubic phase transformed to a monoclinic phase. The maximum bending strength, 313.5MPa, was obtained when 8YSZ was partially destabilized by the addition of 5 mol% Nb2O5. The ionic conductivity also decreased with the increase of Nb2O5 addition. For LaxSr1-xTiO3, the effective charge of LaSr‧ is believed to be compensated by the formation of oxygen interstitials. The expanded perovskite lattice was caused by the introduced oxygen interstitials. Under reducing atmosphere, the lattice parameter of perovskite was reduced. These results suggest that the reduced lattice is caused by the removal of extra oxygen ions. For LaxSr1-3x/2ٱx/2TiO3, the positive charge of LaSr‧ can be compensated by the formation of cation vacancies, VSr//. In this system, the lattice parameter decreases as the La2O3 concentration increases. The conductivity also increases which increasing concentration of La2O3, until the conductivity reaches a maximum at x=0.4. These results indicate that the presence of cation vacancies is the most probable way to compensate the positive charge of LaSr‧. Abstract……………………………………………………………….Ⅲ 目錄…………………………………………………………………….Ⅴ 圖目錄………………………………………………………………….Ⅶ 第一章、 緒論……………………………………………………………1 第二章、 研究動機及目的………………………………………………2 第三章、原理與文獻回顧……………………………………………..4 3-1、高溫固態氧化物燃料電池之簡介…………………………………..4 3-2、固態氧化物燃料電池之陽極材料與陽極反應………………………5 3-3、氧化鈮Nb2O5的添加對釔安定氧化鋯(YSZ，Yttria Stabilized Zirconia)之影響………………………………………………….7 3-4、氧化鑭的添加對於鈦酸鍶之影響………………………………….10 第四章、實驗方法與步驟………………………………………………14 4-1、Nb2O5 doped 8YSZ……………………………………………………14 4-1-1、粉末合成………………………………………………………….14 4-1-2、試片成型………………………………………………………….14 4-1-3、燒結……………………………………………………………….14 4-1-4、XRD分析…………………………………………………………..14 4-1-5、機械強度測試…………………………………………………….16 4-1-6、阿基米得法測試………………………………………………….16 4-1-7、SEM觀察…………………………………………………………..16 4-1-8、導電率測試……………………………………………………….16 4-2、La2O3 doped SrTiO3………………………………………………….18 第五章 Nb2O5的添加對於8YSZ其晶體結構與導電性質之影響…….20 5-1、Nb2O5 doped 8YSZ晶體結構分析…………………………………20 5-2、undoped ZrO2之相變與離子半徑之關係………………………..20 5-3、ZrO2之安定化……………………………………………………..21 5-4、Nb2O5對YSZ的去安定化……………………………………………22 5-5、晶格常數之分析……………………………………………………23 5-5-1、氧空缺位置大小之計算………………………………………..23 5-5-2、Nb2O5的添加對YSZ晶格常數之影響……………………………24 5-6、Nb2O5 doped 8YSZ之破裂模數…………………………………….26 5-7、Nb2O5的添加對8YSZ緻密化之影響……………………………….27 5-8、Nb2O5 doped 8YSZ SEM顯微結構觀察……………………………..28 5-9、Nb2O5 doped 8YSZ 離子導電率測試……………………………..29 第六章、La2O3的添加對SrTiO3其晶體結構與導電性質之影響………43 6-1、LaxSr1-XTiO3系統 ………………………………………………….43 6-1-1、LaxSr1-xTiO3晶體結構分析………………………………………43 6-1-2、La2O3的添加對LaxSr1-xTiO3晶格常數之影響……………………45 6-1-3、La2O3的添加對LaxSr1-xTiO3緻密性之影響…………………….46 6-1-4、La2O3的添加對LaxSr1-xTiO3大氣導電率之影響……………….46 6-1-5、氫氣熱處理對LaxSr1-xTiO3晶格常數之影響……………………47 6-2、LaxSr1-3x/2□x/2TiO3系統…………………………………………….47 6-2-1、LaxSr1-3x/2□x/2TiO3晶體結構分析……………………………….47 6-2-2、La2O3的添加對SrTiO3晶格常數之影響……………………….48 6-2-3、La2O3的添加對SrTiO3緻密性之影響………………………….49 6-2-4、La2O3的添加對SrTiO3大氣導電率之影響……………………..49 6-2-5、氫氣熱處理對La doped SrTiO3晶格常數之影響……………..50 第七章、結論……………………………………………………………68 第八章、參考文獻……………………………………………………..70
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