Cerium and vanadium oxide-based systems play a major role in a variety of technological applications, with the reducibility of the systems being crucial to their functionality in the applications. The in-depth understanding and control of the type, density, and distribution of oxygen vacancies provide a means to influence the electronic structure and to tailor the systems' functionality. Hence, a great deal of experimental and theoretical work has been devoted to the study of partially reduced ceria and vanadia, both surfaces and bulk. Here, theoretical data for structural and electronic properties and energetic quantities related to the formation and interaction of neutral oxygen vacancies at the CeO 2 (111) and V 2 O 5 (001) surfaces are reviewed, discussed and compared. Experimental findings on oxygen defects in ceria and vanadia are briefly reported. Special attention is given to the fate of the electrons left in the system upon vacancy formation, the vacancy-induced lattice relaxation, whether vacancies agglomerate or repel each other, and the ability of state-of-the-art quantum-mechanical methods to provide an accurate decription of the geometric and electronic structures of the partially reduced oxide systems as well as reliable oxygen defect formation energies.
IntroductionReducible metal oxides are extremely functional solid state compounds exhibiting a rich chemistry related to changes of the metal oxidation state [1]. As complex materials such as surfaces, supported particles and films, porous networks, they play a predominant role in applications in advanced technologies like catalysis, sensors, fuel cells, and microelectronics. Point defects in oxides such as vacancies and interstitials account for the transport properties of ionic solids. Defect sites on oxide supports of metal catalyst particles not only act as anchoring and nucleation centers