Ordering of oxygen vacancies and excess charges in reduced ceria

G. E. MURGIDA; M. V. GANDUGLIA PIROVANO; V. FERRARI; A. M. LLOIS

San Sebastián

Conferencia; Psi-k Conference; 2015

The extraordinary ability of ceria to store, release, and transport oxygen is well known and extensively exploited in catalysis and also in other applications, such as nonvolatile memories, logic gates, and fuel cells. The reducibility of the system and the localization of theelectrons left behind upon vacancy formation, driving the Ce 4+ →Ce 3+ reduction, are essential to such applications.To know the ordering of oxygen vacancies and excess charge is crucial to optimize ceria-based materials, but there is still no wide consensus about this subject. To tackle this issue, we use density functional theory in combination with statistical thermodynamics to elucidate thestructure of defective ceria bulk phases [1], Co doped ceria bulk [2], and the reduced CeO 2 (111) surface [3].We find correlations between vacancy− vacancy as well as vacancy− Ce 3+ relative positions and total energies, providing clear indication of the proneness to adopt certain particular relative positions [1], and suggesting a simple model to predict the ordering of excess charge andvacancies in the CeO 2 bulk. For the CeO 2 (111) surface, it is shown that the most stable vacancy structure − under a wide range of reducing conditions− has all its vacancies in the subsurface, forming a (2×2) pattern, as suggested experimentally [4].[1] G.. E. Murgida, V. Ferrari, M. V. Ganduglia-Pirovano, and A. M. Llois, Phys. Rev. B 90, 115120 (2014).[2] G.. E. Murgida, V. Vildosola, V. Ferrari, and A. M. Llois, Solid State Comm. 152, 368 (2012).[3] G.. E. Murgida and M.V. Ganduglia-Pirovano, Phys. Rev. Lett. 110, 246101, (2013).[4] S. Torbrügge, M. Reichling, A. Ishiyama, S. Morita, and O. Custance, Phys. Rev. Lett., 056101 (2007).