Fast oxide-ion conductors in Bi2O3-V2O5 system: Bi108-xVxO162+x(x=4-9) with 3×3×3 superstructure

A Dapcevic,M Zunic,A Radojkovic,G Brankovic,O Milosevic,M Pocuca-Nesic

doi:10.2298/sos2101055d

Abstract

In this study, the possibility to stabilize O2-ion conductors in Bi2O3-V2O5 system was investigated. Six pseudo-binary Bi2O3-V2O5 mixtures [3.50 < x(V2O5) < 8.50 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 ? Bi2O3 and V2O5 resulted in formation of microcrystalline single-phase specimens containing the phase based on ?-Bi2O3 if V2O5 content was ? 4.63 mol%. The obtained phases exhibited main diffraction peaks corresponding to the simple cubic ?-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. Bi 103V5O167, amounts 0.283 S cm-1 at 800?C with the activation energy of 0.64(5) eV, which is comparable to the undoped ?-Bi2O3 known as the fastest ion conductor.

Highlights

The demand for new environmental-friendly technologies for energy production increases the interest in electrolytes based on oxide ion conductors because of their application in solid oxide fuel cells (SOFCs) whose development and widespread use might become a keystone in the near future [1,2,3,4]
The obtained phases exhibited main diffraction peaks corresponding to the simple cubic δ-Bi2O3 but Rietveld refinement showed a threefold repeat on a simple cubic sublattice indicating that the true unit cell is 3×3×3 supercell
The oxide ion conducting materials should possess highly symmetric structure with significant number of oxygen vacancies [5] as it is the case with commercially used yttria stabilized zirconia (YSZ), i. e. the ZrO2 crystallizes in a cubic structure gadolinium-doped ceria (GDC)

Summary

Introduction

The demand for new environmental-friendly technologies for energy production increases the interest in electrolytes based on oxide ion conductors because of their application in solid oxide fuel cells (SOFCs) whose development and widespread use might become a keystone in the near future [1,2,3,4]. The -Bi2O3 polymorph demonstrates one of the highest conductivity, which are one to two orders of magnitude higher than that of YSZ or GDC at corresponding temperatures [12] This is the consequence of highly symmetric pseudo-fluorite structure in which 25 % of oxygen sites are vacant. The thermal treatment of six pseudo-binary Bi2O3-V2O5 mixtures in Bi2O3-rich region [3.5 < x(V2O5) < 8.5 mol%] were investigated in order to find a minimal V concentration that stabilizes δ-Bi2O3 phase down to room temperature giving a highly conductive material that could be used as a functional electrolyte for SOFCs. a new structural model for V-doped δ-Bi2O3 is proposed with the aim to clarify the nature of this superstructure

Materials and Experimental Procedures

Results and Discussion

Conclusion