Influence of Mixed Valence on the Formation of Oxygen Vacancy in Cerium Oxides

Abstract

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.

Long-Range Magnetic Exchange Pathways in Complex Clusters from First Principles

“…Both the Bader charge and the partial magnetic moment confirm the two valence states of the Mn ions. Note that the Bader charges of Mn 3+ and Mn 4+ are small, which is also the case with other ions, such as Ce 3+ and Ce 4+ The partial magnetic moment is calculated by integrating magnetization in spheres surrounding each given ion.…”

“…Note that the Bader charges of Mn 3+ and Mn 4+ are small, which is also the case with other ions, such as Ce 3+ and Ce 4+ The partial magnetic moment is calculated by integrating magnetization in spheres surrounding each given ion. As the Mn ions with J 1 interactions have a different valence, one wonders if double-exchange dominates J 1 , which is a key question of this work and will be discussed in great detail later.…”

First-Principle and Atomistic Modelling in Materials Science

“…The present Special Issue provides a collection of ten articles [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ] and a letter [ 11 ] in which mainly DFT calculations are employed in order to investigate structural, electronic, mechanical and thermal properties. In these papers, well-established computational methods are used to study various properties of potentially promising new materials [ 3 , 4 ] as well as materials interfaces/grain boundaries and their effect on the mechanical behavior [ 8 , 9 , 10 , 11 ].…”

“…The property of the interface between graphene and Al 3 C 4 is determined in Reference [ 11 ]. Furthermore, the behavior, role and influence of intrinsic defects [ 1 , 5 , 6 ] and foreign atoms [ 2 , 6 , 7 ] are investigated, which are traditional topics in computational materials science. The behavior of hydrogen in metals is important for nuclear fusion and also for accelerator-based neutron sources [ 2 , 6 ].…”

“…The behavior of hydrogen in metals is important for nuclear fusion and also for accelerator-based neutron sources [ 2 , 6 ]. On the other hand, the role of vacancies [ 1 ], self-interstitials [ 5 ] and halide atoms [ 7 ] on structural and electronic properties of CeO 2 [ 1 ], GaN [ 5 ], and CsPb(Br 1−x Cl x ) 3 [ 7 ] is investigated. It is worth mentioning that in two excellent papers [ 9 , 11 ] not only original theoretical results are presented but also data obtained by advanced analytical methods such as atomic probe tomography and high-resolution transmission electron microscopy, and a detailed comparison is performed.…”