title: Correlation of Local Structure and Diffusion Pathways in the Modulated Anisotropic Oxide Ion Conductor CeNbO(4.25).
abstract: CeNbO4.25 is reported to exhibit fast oxygen ion diffusion at moderate temperatures, making this the prototype of a new class of ion conductor with applications in a range of energy generation and storage devices. To date, the mechanism by which this ion transport is achieved has remained obscure, in part due to the long-range commensurately modulated structural motif. Here we show that CeNbO4.25 forms with a unit cell ∼12 times larger than the stoichiometric tetragonal parent phase of CeNbO4 as a result of the helical ordering of Ce(3+) and Ce(4+) ions along z. Interstitial oxygen ion incorporation leads to a cooperative displacement of the surrounding oxygen species, creating interlayer "NbO6" connectivity by extending the oxygen coordination number to 7 and 8. Molecular dynamic simulations suggest that fast ion migration occurs predominantly within the xz plane. It is concluded that the oxide ion diffuses anisotropically, with the major migration mechanism being intralayer; however, when obstructed, oxygen can readily move to an adjacent layer along y via alternate lower energy barrier pathways.
authors.affiliation: Department of Materials, Imperial College London , Exhibition Road, London SW7 2AZ, United Kingdom.
authors.forename: Stevin S
authors.initials: SS
authors.lastname: Pramana
authors.forename: Tom
authors.initials: T
authors.lastname: Baikie
authors.forename: Tao
authors.initials: T
authors.lastname: An
authors.affiliation: ISIS Facility, Rutherford Appleton Laboratory , Didcot OX11 0QX, United Kingdom.|Diamond Light Source , Chilton, Oxfordshire, OX11 0DE, United Kingdom.
authors.forename: Matthew G
authors.initials: MG
authors.lastname: Tucker
authors.affiliation: Department of Materials, Imperial College London , Exhibition Road, London SW7 2AZ, United Kingdom.
authors.forename: Ji
authors.initials: J
authors.lastname: Wu
authors.affiliation: Institute of Chemical and Engineering Sciences , 1 Pesek Road, Jurong Island, Singapore.
authors.forename: Martin K
authors.initials: MK
authors.lastname: Schreyer
authors.affiliation: Institute of Materials Research and Engineering , 3 Research Link, Singapore, Singapore.
authors.forename: Fengxia
authors.initials: F
authors.lastname: Wei
authors.affiliation: Department of Materials, Imperial College London , Exhibition Road, London SW7 2AZ, United Kingdom.
authors.forename: Ryan D
authors.initials: RD
authors.lastname: Bayliss
authors.forename: Christian L
authors.initials: CL
authors.lastname: Kloc
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: White
authors.affiliation: Department of Materials, Imperial College London , Exhibition Road, London SW7 2AZ, United Kingdom.
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Horsfield
authors.affiliation: Department of Materials, Imperial College London , Exhibition Road, London SW7 2AZ, United Kingdom.
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Skinner