Fast Oxide-Ion Conductors in Bi2O3-V2O5 System: Bi108-xVxO162+x(x=4-9) with 3 x 3 x 3 Superstructure

Abstract

In this study, the possibility to stabilize O-2 ion conductors in Bi2O3-V2O5 system was investigated. Six pseudo-binary Bi2O3-V2O5 mixtures [3.50 lt x(V2O5) lt 8.50 mol%] were thermally treated at 1000 degrees C for 1 h. The samples were characterized by XRD, HRTEM/SAED, DTA and EIS techniques. The high-temperature reaction between alpha Bi2O3 and V2O5 resulted in formation of microcrystalline single-phase specimens containing the phase based on delta-Bi2O3 if V2O5 content was >= 4.63 mol%. The obtained phases exhibited main diffraction peaks corresponding to the simple cubic delta-Bi2O3 (space group Fm-3m) but Rietveld refinement showed a threefold repeat on a simple cubic sublattice indicating that the true unit cell is 3x3x3 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 degrees C with the activation energy of 0.64(5) eV, which is comparable to the undoped delta-Bi2O3 known as the fastest ion conductor.