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SUMMARY:Optimization of ionic conductivity in doped ceria - Nick Bristowe 
 (TCM)
DTSTART:20090206T153000Z
DTEND:20090206T160000Z
UID:TALK16255@talks.cam.ac.uk
CONTACT:Daniel Cole
DESCRIPTION:"Andersson _et al_\, PNAS 103\, 3518-3521\, 2006":http://www.p
 nas.org/content/103/10/3518\n\nOxides with the cubic fluorite structure\, 
 e.g.\, ceria (CeO2)\, are known to be good solid electrolytes when they ar
 e doped with cations of lower valence than the host cations. The high ioni
 c conductivity of doped ceria makes it an attractive electrolyte for solid
  oxide fuel cells\, whose prospects as an environmentally friendly power s
 ource are very promising. In these electrolytes\, the current is carried b
 y oxygen ions that are transported by oxygen vacancies\, present to compen
 sate for the lower charge of the dopant cations. Ionic conductivity in cer
 ia is closely related to oxygen-vacancy formation and migration properties
 . A clear physical picture of the connection between the choice of a dopan
 t and the improvement of ionic conductivity in ceria is still lacking. Her
 e we present a quantum-mechanical first-principles study of the influence 
 of different trivalent impurities on these properties. Our results reveal 
 a remarkable correspondence between vacancy properties at the atomic level
  and the macroscopic ionic conductivity. The key parameters comprise migra
 tion barriers for bulk diffusion and vacancy–dopant interactions\, repre
 sented by association (binding) energies of vacancy–dopant clusters. The
  interactions can be divided into repulsive elastic and attractive electro
 nic parts. In the optimal electrolyte\, these parts should balance. This f
 inding offers a simple and clear way to narrow the search for superior dop
 ants and combinations of dopants. The ideal dopant should have an effectiv
 e atomic number between 61 (Pm) and 62 (Sm)\, and we elaborate that combin
 ations of Nd/Sm and Pr/Gd show enhanced ionic conductivity\, as compared w
 ith that for each element separately.
LOCATION:TCM Seminar Room\, Cavendish Laboratory
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