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Oxygen vacancy clusters on ceria: Decisive role of cerium f electrons Changjun Zhang,1 Angelos Michaelides,2 David A. King,1 and Stephen J. Jenkins1,*
 

Summary: Oxygen vacancy clusters on ceria: Decisive role of cerium f electrons
Changjun Zhang,1 Angelos Michaelides,2 David A. King,1 and Stephen J. Jenkins1,*
1Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom
2Department of Chemistry, Materials Simulation Laboratory, and London Centre for Nanotechnology, University College London,
London WC1H 0AH, United Kingdom
Received 27 November 2008; published 20 February 2009
Defects such as oxygen vacancies dominate the electronic and chemical properties of ceria. However,
fundamental understanding of such defects, especially clusters of vacancies, is sparse. In this work, we use
density-functional theory with the addition of the Hubbard U term to investigate various oxygen vacancies,
including the vacancy monomer, dimer, trimer, and tetramer, in which subsurface vacancies can also be
involved. We show that the individual surface and subsurface vacancies have very similar stabilities; the
vacancy dimer consisting of two surface vacancies, which is not reported experimentally, is stable in theory;
between the two vacancy trimers observed in experiments, the triangular surface vacancy cluster is more stable
than the double linear surface vacancy cluster containing a subsurface vacancy, which agrees with some
experiments but disagrees with some others; and the linear vacancy tetramer emerges as the most stable among
the possible tetramers containing subsurface vacancies, although it is less stable than those containing no
subsurface vacancies. These findings are rationalized in terms of the electronic change upon the removal of
oxygen, namely, the localization of resulting excess electrons on Ce f orbitals. We identify a correlation
between the energy levels of the occupied f states of reduced Ce ions and their coordination numbers, which
proves pivotal in interpreting formation energy and stability of various vacancies. Comparisons are made with

  

Source: Alavi, Ali - Department of Chemistry, University of Cambridge

 

Collections: Chemistry