Fast Oxide-Ion Conductors in Bi2O3-V2O5 System: Bi(108-x)VxO(162+x) (x = 4–9) with 3 × 3 × 3 Superstructure
In this study, the possibility to stabilize O2– ion conductors in Bi2O3-V2O5 system was investigated. Six pseudo-binary Bi2O3-V2O5 mixtures [x(V2O5) = 3.5-8.5 mol%] were thermally treated at 1000 °C for 1 h. The samples were characterized by XRD, HRTEM/SAED, DTA and EIS techniques. The high-temperature reaction between α Bi2O3 and V2O5 resulted in formation of microcrystalline single-phase specimens containing the phase based on δ-Bi2O3 if V2O5 content was ≥ 4.63 mol%. The obtained phases exhibited main diffraction peaks corresponding to the simple cubic δ-Bi2O3 (space group Fm-3m) but Rietveld refinement showed a threefold repeat on a simple cubic sublattice indicating that the true unit cell is 3×3×3 supercell. Within proposed supercell, the octahedrally coordinated V5+ ions fully occupy 4a Wyckoff position and partially occupy 32f. The Bi3+ ions are placed at the rest of 32f and at 24e and 48h with full occupation. In total, 22 % of anionic sites are vacant. The ionic conductivity of phase with the lowest dopant content, i.e. Bi103V5O167, amounts 0.283 S cm–1 at 800 °C with the activation energy of 0.64(5) eV, which is comparable to the undoped δ-Bi2O3 known as the fastest ion conductor.
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