Influence of Mixed Valence on the Formation of Oxygen Vacancy in Cerium Oxides
Influence of Mixed Valence on the Formation of Oxygen Vacancy in Cerium Oxides
复制标题
混合价态对氧化铈中氧空位形成的影响
DOI：
10.3390/ma12244041
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发表时间：
2019-12-02
期刊：
影响因子：
3.4
通讯作者：
Wang, Ligen
中科院分区：
文献类型：
--
作者：
Zhou, Gege;Geng, Wentong;Wang, Ligen
二氧化铈是一种重要的功能稀土氧化物，具有广泛的工业用途。其惊人的氧储存/释放能力归功于铈在4+和3+之间灵活的价转换。然而，价转换究竟是由于Ce-4f电子的定域-离域跃迁，还是Ce-O共价键的性质，仍然存在一些争论。本文建立了一个混合价模型，并通过密度泛函理论计算得到了氧空位和电子电荷的形成能。结果表明，氧空位的形成能受到邻近Ce原子价态的影响，CeO2中Ce4+周围的两个氧空位对Ce3+的影响与Ce3+相似。Ce3+和Ce4+的电荷差仅为0.4e左右。因此，我们认为价转换应该根据共价键与离子键比值的调整来理解。我们提出用氧空位的形成能作为描述符来确定铈氧化物中Ce的价态。
Ceria is one of the most important functional rare-earth oxides with wide industrial applications. Its amazing oxygen storage/release capacity is attributed to cerium's flexible valence conversion between 4+ and 3+. However, there still exists some debate on whether the valence conversion is due to the Ce-4f electron localization-delocalization transition or the character of Ce-O covalent bonds. In this work, a mixed valence model was established and the formation energies of oxygen vacancies and electronic charges were obtained by density functional theory calculations. Our results show that the formation energy of oxygen vacancy is affected by the valence state of its neighboring Ce atom and two oxygen vacancies around a Ce4+ in CeO2 have a similar effect to a Ce3+. The electronic charge difference between Ce3+ and Ce4+ is only about 0.4e. Therefore, we argue that the valence conversion should be understood according to the adjustment of the ratio of covalent bond to ionic bond. We propose that the formation energy of oxygen vacancy be used as a descriptor to determine the valence state of Ce in cerium oxides.