| 1. |
- Abrahams, I., et al.
(författare)
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A Combined Total Scattering and Simulation Approach to Analyzing Defect Structure in Bi3YO6
- 2010
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 1520-5002 .- 0897-4756. ; 22:15, s. 4435-4445
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Tidskriftsartikel (refereegranskat)abstract
- The defect structure and electrical properties of the fast oxide ion-conducting solid electrolyte delta-Bi3YO6 have been studied using a combination of total neutron scattering analysis, energy minimization methods, and AC impedance spectroscopy. Conventional structural analysis using the Rietveld method reveals the oxide ions to be distributed over three crystallographic sites at room temperature, with a small change in this distribution at 800 degrees C. Analysis of short-range correlations using a total neutron scattering approach yields information on Bi and Y coordination environments. Careful analysis of the angular distribution functions derived from reverse Monte Carlo modeling of the total scattering data reveals physical evidence for a predominance of vacancy ordering in this system. This ordering is confirmed as the lowest energy configuration in parallel energy minimization simulations.
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| 2. |
- Leszczynska, M., et al.
(författare)
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Oxide ion distribution, vacancy ordering and electrical behaviour in the Bi3NbO7-Bi3YbO6 pseudo-binary system
- 2014
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 2:43, s. 18624-18634
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Tidskriftsartikel (refereegranskat)abstract
- Oxide ion distribution, vacancy ordering and electrical conductivity has been examined in the Nb/Yb double substituted bismuth oxide based system Bi3Nb1-xYbxO7-x, using X-ray and neutron powder diffraction, reverse Monte Carlo modelling of total neutron scattering data and a. c. impedance spectroscopy. Transference number measurements confirm the system to be predominantly ionically conducting above ca. 450 degrees C. Niobium rich compositions show incommensurate ordering of the fluorite subcell, while increasing ytterbium content results in a commensurate fluorite, with fully disordered cation and anion sublattices. Oxide ion distribution shows both compositional and thermal dependencies. The latter is discussed with respect to its effect on the thermal variation of cubic lattice parameter. Substitution of bismuth by niobium and ytterbium in the cation sublattice of bismuth oxide leads to the creation of Frenkel interstitial oxide ions, which increase the tetrahedral vacancy concentration. The high vacancy concentration is confirmed in both Rietveld and RMC analyses of neutron data. Examination of vacancy ordering, in the x - 0.6 composition, indicates a favouring of vacancy pair alignment.
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| 3. |
- Leszczynska, M., et al.
(författare)
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Thermal Variation of Structure and Electrical Conductivity in Bi4YbO7.5
- 2013
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 1520-5002 .- 0897-4756. ; 25:3, s. 326-336
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Tidskriftsartikel (refereegranskat)abstract
- The thermal behavior of the oxide ion-conducting solid electrolyte Bi4YbO7.5 was investigated using a combination of variable temperature X-ray and neutron powder diffraction, thermal analysis (DTA and TGA), and ac impedance spectroscopy. The title compound shows a fluorite-type structure throughout the measured temperature range (20-850 degrees C), with a phase separation at ca. 600 degrees C into a cubic delta-type phase and an orthorhombic phase of assumed stoichiometry Bi17Yb7O36. This type of transition is a relatively common feature in bismuth oxide-based systems and can limit their practical application. Here, the transition was carefully studied using isothermal measurements, which showed that it is accompanied by changes in oxide-ion stoichiometry, as well as significant disorder in the oxide ion sublattice in the delta-type phase. These results correlate with the observed electrical behavior. Analysis of the total neutron scattering through reverse Monte Carlo (RMC) modeling reveals details of the coordination environments for both cations. The oxide-ion vacancy distribution seems to be consistent with a favoring of vacancy pairs, although vacancy pairs exhibit the highest frequency as they have the maximum likelihood. A vacancy ordering model based on three vacancies per cell is presented.
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| 4. |
- Leszczynska, M., et al.
(författare)
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Total scattering analysis of cation coordination and vacancy pair distribution in Yb substituted delta-Bi2O3
- 2013
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Ingår i: Journal of Physics Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 25:45
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Tidskriftsartikel (refereegranskat)abstract
- Reverse Monte Carlo (RMC) modelling of neutron total scattering data, combined with conventional Rietveld analysis of x-ray and neutron data, has been used to describe the cation coordination environments and vacancy pair distribution in the oxide ion conducting electrolyte Bi3YbO6. The thermal variation of the cubic fluorite unit cell volume, monitored by variable temperature x-ray and neutron experiments, reveals significant curvature, which is explained by changes in the oxide ion distribution. There is a significant increase in tetrahedral oxide ion vacancy concentration relative to delta-Bi2O3, due to the creation of Frenkel defects associated with the Yb3+ cation. The tetrahedral oxide ion vacancy concentration increases from room temperature to 800 degrees C, but little change is observed in the vacancy pair distribution with temperature. The vacancy pair distributions at both temperatures are consistent with a favouring of vacancy pairs.
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| 5. |
- Liu, X., et al.
(författare)
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A neutron total scattering study of defect structure in Bi3Nb0.5Y0.5O6.5
- 2011
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Ingår i: Solid State Ionics. - : Elsevier BV. - 0167-2738. ; 192:1, s. 176-180
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Tidskriftsartikel (refereegranskat)abstract
- The defect structure of the title compound has been analyzed by reverse Monte Carlo (RMC) modeling of neutron total scattering data. The composition exhibits both diffuse scattering and weak superlattice ordering of the cubic fluorite subcell in neutron diffraction patterns. Combined Rietveld analysis of X-ray and neutron data at room temperature reveals oxide ion scattering on three crystallographic sites. Analysis of the RMC model reveals Bi coordination numbers consistent with stereochemical activity of the Bi 6 s(2) lone pair electrons. Integration of the O-M-O angular distribution function gives an angular ratio consistent with predominantly vacancy ordering in this system.
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