Institute of Physical Chemistry, RWTH Aachen University and JARA-HPC, Landoltweg 2, 52056 Aachen, Germany.
Phys Chem Chem Phys. 2013 Oct 14;15(38):15935-42. doi: 10.1039/c3cp51913a. Epub 2013 Aug 16.
We calculate entropies of formation for fully charged point defects, including the small polaron Ce'(Ce), in undoped fluorite-structured ceria by means of density functional theory in the GGA + U approximation. We discuss the behaviour of the entropy for the constant volume and the constant pressure case. Our results for constant pressure (p = 0) suggest that the change in volume, due to the formation of defects, dominates the entropy of formation. From the individual entropies of formation the entropies of Frenkel, anti-Frenkel and Schottky disorder as well as the entropy of reduction of ceria are obtained. At temperatures of about 1000 K the entropic contributions to the Gibbs energy are up to 0.9 eV per defect and thus are no longer negligible. For our calculated entropy of reduction of about 17 kB we find a remarkable agreement with experimental data from the literature.
我们通过 GGA + U 近似的密度泛函理论计算了完全充电点缺陷（包括小极化子 Ce'（Ce））在未掺杂萤石结构氧化铈中的生成焓。我们讨论了等容和等压情况下熵的行为。我们对等压（p = 0）的结果表明，由于缺陷的形成导致的体积变化主导了生成焓的熵。从各个生成焓中，我们得到了 Frenkel、反 Frenkel 和 Schottky 无序以及氧化铈还原的熵。在约 1000 K 的温度下，每个缺陷的吉布斯自由能的熵贡献高达 0.9 eV，因此不再可以忽略不计。对于我们计算出的还原熵约为 17 kB，我们发现与文献中的实验数据有显著的一致性。
