Arrangement of oxygen vacancies and excess charges in CeO 2 reduced bulk and surface

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

La Plata

Workshop; Workshop on Novel Methods for Electronic Structure Calculations; 2015

The importance of ceria (CeO 2 ) in many applicatons originates from the easy of oxygen formation vacancy and healing through the reversible CeO 2 ↔CeO 2−δ ↔ Ce 2 O 3 reduction. In addition, the localization of vacancies and of the electrons left behind upon vacancy formation, driving the Ce 4+ → Ce 3+ reduction, are essential to such applications. We tackle this issue using DFT+U approach (PBE+U=4.5eV and VASP code) in combination with statistical thermodynamics to elucidate the structure of defective ceria bulk phases [1], reduced CeO 2 (111) surface [2], and Co doped bulk ceria [3].We find correlations between vacancy-vacancy as well as vacancy-Ce 3+ relative positions and total energies, providing clear indication of the proneness of vacancies and Ce 3 + to adopt certain configurations [1]. Such correlations are at the basis of a proposed simple model to predictthe ordering of excess charge and vacancies in bulk CeO 2 that enables the separation of the different contributions to the total energy. For the CeO 2 (111) surface [2], it is shown that for a wide range of near-surface vacancy concentrations, the energetically most stable structures have all the vacancies localized in the second oxygen layer. Moreover, we found that that under a wide range of reducing conditions, a (2×2) ordered subsurface vacancy structure is stable, pro-viding support for recent experimental results [4]. Defect-induced lattice relaxations are used to explain the findings.[1] G. E. Murgida, V. Ferrari, M. V. Ganduglia-Pirovano, and A. M. Llois, Phys. Rev. B 90,115120 (2014).[2] G. E. Murgida and M.V. Ganduglia-Pirovano, Phys. Rev. Lett. 110, 246101, (2013).[3] G. E. Murgida, V. Vildosola, V. Ferrari, and A. M. Llois, Solid State Comm. 152, 368(2012).[4] S. Torbrügge, M. Reichling, A. Ishiyama, S. Morita, and O. Custance, Phys. Rev. Lett.90,056101 (2007).