title: Pseudotetragonal structure of Li(2+x)Ce(x)(3+)Ce(12-x)(4+)F(50): the first mixed valence cerium fluoride.
abstract: The crystal structure of the new Li(5.5)Ce(12)F(50) compound has been fully characterized by single-crystal and synchrotron powder X-ray diffraction. An accurate pseudotetragonal structure was described in the monoclinic P2(1) space group with 68 independent crystallographic sites. The Li(5.5)Ce(12)F(50) composition belongs to the Li(2+x)Ce(x)(3+)Ce(12-x)(4+)F(50) solid solution. Its structure consists of an opened fluorine framework where a channel network allows the intercalation of relatively mobile lithium cations, inducing the formation of the mixed-valence cerium (the intercalation of Li(+) leads to the reduction of a part of Ce(4+) to Ce(3+)). One part of the lithium ions, necessary for the electroneutrality of the tetravalent equivalent cerium fluoride (Li(2)Ce(12)F(50) composition), is in a locked fluorine polyhedron. Only the supplementary x amount of lithium is able to be exchanged in Li(2+x)Ce(x)(3+)Ce(12-x)(4+)F(50). The structure of Li(2+x)Ce(x)(3+)Ce(12-x)(4+)F(50) is a rearrangement, due to lithium intercalation, of the base CeF(4) structure. Bond valence calculation on Ce sites, Ce coordination polyhedra volumes, and a calculated Ce cationic radius give the indication of a partial long-range ordering of trivalent and tetravalent cerium cations in specific slabs of the structure. (7)Li NMR spectroscopy and XPS analyses have confirmed all of the structure details.
authors.affiliation: Clermont Université, ENSCCF, Laboratoire des Matériaux Inorganiques, BP 10448, F-63000 Clermont-Ferrand, France. guillaume.renaudin@ensccf.fr
authors.forename: Guillaume
authors.initials: G
authors.lastname: Renaudin
authors.forename: Belto
authors.initials: B
authors.lastname: Dieudonné
authors.forename: Daniel
authors.initials: D
authors.lastname: Avignant
authors.forename: Elise
authors.initials: E
authors.lastname: Mapemba
authors.forename: Malika
authors.initials: M
authors.lastname: El-Ghozzi
authors.forename: Solène
authors.initials: S
authors.lastname: Fleutot
authors.forename: Hervé
authors.initials: H
authors.lastname: Martinez
authors.forename: Radovan
authors.initials: R
authors.lastname: Cerný
authors.forename: Marc
authors.initials: M
authors.lastname: Dubois