Andersson David A, Simak Sergei I, Skorodumova Natalia V, Abrikosov Igor A, Johansson Börje
Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology, SE-100 44 Stockholm, Sweden.
Proc Natl Acad Sci U S A. 2006 Mar 7;103(10):3518-21. doi: 10.1073/pnas.0509537103. Epub 2006 Feb 14.
Oxides with the cubic fluorite structure, e.g., ceria (CeO2), are known to be good solid electrolytes when they are doped with cations of lower valence than the host cations. The high ionic conductivity of doped ceria makes it an attractive electrolyte for solid oxide fuel cells, whose prospects as an environmentally friendly power source are very promising. In these electrolytes, the current is carried by oxygen ions that are transported by oxygen vacancies, present to compensate for the lower charge of the dopant cations. Ionic conductivity in ceria is closely related to oxygen-vacancy formation and migration properties. A clear physical picture of the connection between the choice of a dopant and the improvement of ionic conductivity in ceria is still lacking. Here we present a quantum-mechanical first-principles study of the influence of different trivalent impurities on these properties. Our results reveal a remarkable correspondence between vacancy properties at the atomic level and the macroscopic ionic conductivity. The key parameters comprise migration barriers for bulk diffusion and vacancy-dopant interactions, represented by association (binding) energies of vacancy-dopant clusters. The interactions can be divided into repulsive elastic and attractive electronic parts. In the optimal electrolyte, these parts should balance. This finding offers a simple and clear way to narrow the search for superior dopants and combinations of dopants. The ideal dopant should have an effective atomic number between 61 (Pm) and 62 (Sm), and we elaborate that combinations of Nd/Sm and Pr/Gd show enhanced ionic conductivity, as compared with that for each element separately.
具有立方萤石结构的氧化物，例如二氧化铈（CeO₂），当用比主体阳离子价态低的阳离子进行掺杂时，已知是良好的固体电解质。掺杂二氧化铈的高离子电导率使其成为固体氧化物燃料电池有吸引力的电解质，其作为环境友好型电源的前景非常广阔。在这些电解质中，电流由氧离子携带，氧离子通过氧空位传输，氧空位的存在是为了补偿掺杂阳离子较低的电荷。二氧化铈中的离子电导率与氧空位的形成和迁移特性密切相关。目前仍缺乏关于掺杂剂选择与二氧化铈中离子电导率提高之间联系的清晰物理图像。在此，我们对不同三价杂质对这些性质的影响进行了量子力学第一性原理研究。我们的结果揭示了原子水平上空位性质与宏观离子电导率之间的显著对应关系。关键参数包括体扩散的迁移势垒和空位 - 掺杂剂相互作用，由空位 - 掺杂剂团簇的缔合（结合）能表示。这些相互作用可分为排斥性弹性部分和吸引性电子部分。在最佳电解质中，这些部分应达到平衡。这一发现为缩小寻找优质掺杂剂和掺杂剂组合的范围提供了一种简单明了的方法。理想的掺杂剂有效原子序数应在61（钷）和62（钐）之间，并且我们详细阐述了与单独的每种元素相比，钕/钐和镨/钆的组合显示出增强的离子电导率。
