Structures of oxygen vacancies on surface and bulk CeO$_2$: A DFT+U study

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

Trieste

Conferencia; Conference: What about U? - Effects of Hubbard Interactions and Hund?s Coupling in Solids (smr 2827); 2016

ICTP

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 nonvolatilememories, logic gates, and fuel cells. The reducibility of the system and the localization of the electrons 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 tooptimize ceria based materials. We use 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], 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, and suggesting a simple model to predict the ordering of excess charge and vacancies in the CeO_2 bulk. For the CeO_2(111) surface, we find that two experimentally reported reconstructions, 3 x 3 and $\sqrt 3 \times \sqrt 3$, can be explained as terminations of a meta-stable bulk structure of Ce_3O_5 which we propose in this job but that yet have not been observed.