First-principles study on defect chemistry and migration of oxide ions in ceria doped with rare-earth cations.
First-principles study on defect chemistry and migration of oxide ions in ceria doped with rare-earth cations.
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DOI：
10.1039/b900162j
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发表时间：
2009-04
期刊：
影响因子：
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通讯作者：
M. Nakayama;Manfred Martin
中科院分区：
文献类型：
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作者：
M. Nakayama;Manfred Martin
具有萤石结构的稀土氧化物（RE（2）O（3））掺杂CeO（2）中的氧输运由于其实际应用范围（例如，燃料电池、传感器等）以及晶体固体中快速氧离子传输的基本魅力。用密度泛函理论计算了RE（2）O（3）掺杂CeO（2）（RE = Sc，Y，La，Nd，Sm，Gd，Dy，Lu）中点缺陷的形成能及其迁移特性。计算结果表明，RE（3+）掺杂的缺陷物种主要是氧空位。它们与RE（3+）离子形成缔合物，相应的缺陷缔合能是RE（3+）掺杂剂离子半径的强函数。采用轻推弹性带方法研究了氧空位的迁移。氧空位跳跃的最低激活能是由两个相邻的氧位点之间的直接迁移路径获得的。氧空位的迁移能也强烈依赖于相邻掺杂剂阳离子的离子半径。因此，我们已经确定了影响氧空位迁移的两个因素：（1）在RE（3+）掺杂剂的NN位置处捕获（或排斥）氧空位，以及（2）通过RE（3+）掺杂降低（或扩大）迁移势垒。这些发现提供了深入的原子水平的理解离子电导率在掺杂氧化铈和优化离子电导率将是有益的。
Oxygen transport in rare-earth oxide (RE(2)O(3)) doped CeO(2) with fluorite structure has attracted considerable attention owing to both the range of practical usage (e.g., fuel cells, sensors, etc.) and the fundamental fascination of fast oxide ion transport in crystalline solids. Using density-functional theory, we have calculated the formation energies of point defects and their migration properties in RE(2)O(3) doped CeO(2)(RE = Sc, Y, La, Nd, Sm, Gd, Dy, and Lu). The calculated results show that oxygen vacancies are the dominant defect species obtained by RE(3+) doping. They form associates with the RE(3+) ions, and the corresponding defect association energy is a strong function of the ionic radii of the RE(3+) dopants. The migration of an oxygen vacancy was investigated using the nudged elastic band method. The lowest activation energy for oxygen vacancy hopping is obtained for a straightforward migration path between two adjacent oxygen sites. The migration energy of an oxygen vacancy also strongly depends on the ionic radii of the neighbouring dopant cations. Accordingly, we have identified two factors that affect the oxygen vacancy migration; (1) trapping (or repelling) of an oxygen vacancy at the NN site of the RE(3+) dopant, and (2) reduction (or enlargement) of the migration barrier by RE(3+) doping. These findings provide insight for atomistic level understanding of ionic conductivity in doped ceria and would be beneficial for optimizing ionic conductivity.