The key role of the composition and structural features in fluoride ion conductivity in tysonite Ce1-xSrxF3-x solid solutions.

Belto Dieudonné (1) , Johann Chable (1, 2) , Monique Body (2) , Christophe Legein (2) , Etienne Durand (1) , Fabrice Mauvy (1) , Sébastien Fourcade (1) , Marc Leblanc (2) , Vincent Maisonneuve (2) , Alain Demourgues (1)

1 ICMCB - Institut de Chimie de la Matière Condensée de Bordeaux
2 IMMM - Institut des Molécules et Matériaux du Mans

Pure tysonite-type Ce1-xSrxF3-x solid solutions for 0 ≤ x < 0.15 were prepared by a solid-state route at 900 °C. The cell parameters follow Vegard's laws for 0 ≤ x ≤ 0.10 and the solubility limit is identified (0.10 < xlimit < 0.15). For 0 ≤ x ≤ 0.05, the F2-(Ce,Sr) and F3-(Ce,Sr) bond distances into [Ce1-xSrxF]((2-x)+) slabs strongly vary with x. This slab buckling is maximum around x = 0.025 and strongly affects the more mobile F1 fluoride ions located between the slabs. The (19)F MAS NMR spectra show the occurrence of F1-F2,3 exchange at 64 °C. The fraction of mobile F2,3 atoms deduced from the relative intensity of the NMR resonance is maximum for Ce0.99Sr0.01F2.99 (22% at 64 °C) while this fraction linearly increases with x for La1-xAExF3-x (AE = Ba, Sr). The highest conductivity found for Ce0.975Sr0.025F2.975 (3 × 10(-4) S cm(-1) at RT, Ea = 0.31 eV) is correlated to the largest dispersion of F2-(Ce,Sr) and F3-(Ce,Sr) distances which induces the maximum sheet buckling. Such a relationship between composition, structural features and fluoride ion conductivity is extended to other tysonite-type fluorides. The key role of the difference between AE(2+) and RE(3+) ionic radii and of the thickness of the slab buckling is established and could allow designing new ionic conductors.

Domaines: Matériaux

Belto Dieudonné, Johann Chable, Monique Body, Christophe Legein, Etienne Durand, et al.. The key role of the composition and structural features in fluoride ion conductivity in tysonite Ce1-xSrxF3-x solid solutions.. Dalton Transactions, 2017, 46 (11), pp.3761-3769. ⟨10.1039/c6dt04714a⟩. ⟨hal-01503538⟩