title: Structure and segregation of dopant-defect complexes at grain boundaries in nanocrystalline doped ceria.
abstract: Grain boundaries (GBs) dictate vital properties of nanocrystalline doped ceria. Thus, to understand and predict its properties, knowledge of the interaction between dopant-defect complexes and GBs is crucial. Here, we report atomistic simulations, corroborated with first principles calculations, elucidating the fundamental dopant-defect interactions at model GBs in gadolinium-doped and manganese-doped ceria. Gadolinium and manganese are aliovalent dopants, accommodated in ceria via a dopant-defect complex. While the behavior of isolated dopants and vacancies is expected to depend on the local atomic structure at GBs, the added structural complexity associated with dopant-defect complexes is found to have key implications on GB segregation. Compared to the grain interior, energies of different dopant-defect arrangements vary significantly at the GBs. As opposed to bulk, the stability of oxygen vacancy is found to be sensitive to the dopant arrangement at GBs. Manganese exhibits a stronger propensity for segregation to GBs than gadolinium, revealing that accommodation of dopant-defect clusters depends on the nature of dopants. Segregation strength is found to depend on the GB character, a result qualitatively supported by our experimental observations based on scanning transmission electron microscopy. The present results indicate that segregation energies, availability of favorable sites, and overall stronger binding of dopant-defect complexes would influence ionic conductivity across GBs in nanocrystalline doped ceria. Our comprehensive investigation emphasizes the critical role of dopant-defect interactions at GBs in governing functional properties in fluorite-structured ionic conductors.
authors.affiliation: Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA. pdholabhai@lanl.gov.
authors.forename: Pratik P
authors.initials: PP
authors.lastname: Dholabhai
authors.forename: Jeffery A
authors.initials: JA
authors.lastname: Aguiar
authors.forename: Longjia
authors.initials: L
authors.lastname: Wu
authors.forename: Terry G
authors.initials: TG
authors.lastname: Holesinger
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Aoki
authors.forename: Ricardo H R
authors.initials: RH
authors.lastname: Castro
authors.forename: Blas P
authors.initials: BP
authors.lastname: Uberuaga