- Insight into Design of Improved Oxide Ion Conductors: Dynamics and Conduction Mechanisms in the Bi0.913V0.087O1.587 Solid Electrolyte
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Extensive quasielastic neutron scattering measurements have been used to directly observe oxide ion dynamics on the nanosecond time scale in bismuth vanadate with formula Bi0.913V0.087O1.587, which exhibits remarkable oxide ion conductivity at low temperatures. This is the longest time scale neutron scattering study of any fluorite-type solid electrolyte, and it represents only the second case of oxide ion dynamics in any material observed on a nanosecond time scale by quasielastic neutron scattering. Ab initio molecular dynamics simulations reveal two mechanisms that contribute to the oxide ion dynamics in the material: a slower diffusion process through the Bi-O sublattice and a faster process which corresponds to more localized dynamics of the oxide ions within the VOx coordination spheres. The length of the trajectories simulated and the validation of the simulations by neutron scattering experiments provide for the first time a quantitative insight into the relative contributions of the two processes to the oxide ion conduction in this exceptional solid electrolyte, which can be used to derive design principles for the preparation of related oxide ion conductors with even better properties.
- Peet, Joseph R.,Fuller, Chloe A.,Frick, Bernhard,Koza, Michael M.,Johnson, Mark R.,Piovano, Andrea,Evans, Ivana Radosavljevic
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- Variable-Temperature Multinuclear Solid-State NMR Study of Oxide Ion Dynamics in Fluorite-Type Bismuth Vanadate and Phosphate Solid Electrolytes
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Ionic conducting materials are crucial for the function of many advanced devices used in a variety of applications, such as fuel cells and gas separation membranes. Many different chemical controls, such as aliovalent doping, have been attempted to stabilize ?-Bi2O3, a material with exceptionally high oxide-ion conductivity which is unfortunately only stable over a narrow temperature range. In this study, we employ a multinuclear, variable-temperature NMR (VT-NMR) spectroscopy approach to characterize and measure oxide-ionic motion in the V- and P-substituted bismuth oxide materials Bi0.913V0.087O1.587, Bi0.852V0.148O1.648, and Bi0.852P0.148O1.648, previously shown to have excellent ionic conduction properties (Kuang et al., Chem. Mater. 2012, 24, 2162; Kuang et al., Angew. Chem., Int. Ed. 2012, 51, 690). Two main 17O NMR resonances are distinguished for each material, corresponding to O in the Bi-O and V-O/P-O sublattices. Using VT measurements ranging from room temperature to 923 K, the ionic motion experienced by these different sites has then been characterized, with coalescence of the two environments in the V-substituted materials clearly indicating a conduction mechanism facilitated by exchange between the two sublattices. The lack of this coalescence in the P-substituted material indicates a different mechanism, confirmed by 17O T1 (spin-lattice relaxation) NMR experiments to be driven purely by vacancy motion in the Bi-O sublattice. 51V and 31P VT-NMR experiments show high rates of tetrahedral rotation even at room temperature, increasing with heating. An additional VO4 environment appears in 17O and 51V NMR spectra of the more highly V-substituted Bi0.852V0.148O1.648, which we ascribe to differently distorted VO4 tetrahedral units that disrupt the overall ionic motion, consistent both with line width analysis of the 17O VT-NMR spectra and experimental results of Kuang et al., showing a lower oxide-ionic conductivity in this material compared to Bi0.913V0.087O1.587 (Chem. Mater. 2012, 24, 2162). This study shows that solid-state NMR is particularly well suited to understanding connections between local structural features and ionic mobility and can quantify the evolution of oxide-ion dynamics with increasing temperature.
- Dunstan, Matthew T.,Halat, David M.,Tate, Matthew L.,Evans, Ivana Radosavljevic,Grey, Clare P.
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- Remarkably high oxide ion conductivity at low temperature in an ordered fluorite-type superstructure
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Mobile oxide ions: A remarkably high oxide ion conductivity at low temperatures has been found in an ordered δ-Bi2O3 superstructure with the composition Bi1-xVxO 1.5+x (x=0.087 and 0.095), and attributed to a combination of highly polarizable sublattice with vacancies, central atoms able to support variable coordination numbers and geometries, as well as rotational flexibility of these coordination polyhedra, co-existing in a pseudo-cubic structure (see picture). Copyright
- Kuang, Xiaojun,Payne, Julia L.,Johnson, Mark R.,Radosavljevic, Ivana Evans
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- Insight into Design of Improved Oxide Ion Conductors: Dynamics and Conduction Mechanisms in the Bi0.913V0.087O1.587 Solid Electrolyte
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Extensive quasielastic neutron scattering measurements have been used to directly observe oxide ion dynamics on the nanosecond time scale in bismuth vanadate with formula Bi0.913V0.087O1.587, which exhibits remarkable oxid
- Peet, Joseph R.,Fuller, Chloe A.,Frick, Bernhard,Koza, Michael M.,Johnson, Mark R.,Piovano, Andrea,Evans, Ivana Radosavljevic
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p. 9989 - 9997
(2019/07/05)
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