Enhanced Phase Stability and Oxide-Ion Conductivity in V- and Sr/Ca-Codoped Bi₂O₃ Ceramics

Herein, highly stable and exceptionally high oxide-ion conducting vanadium- and strontium/calcium-codoped bismuth oxides of Bi0.893Sr0.02V0.087O1.577 (BSV0.087O) and Bi0.893Ca0.02V0.087O1.577 (BCV0.087O) have been reported. Both materials exhibit conductivity values of ∼10–3 S/cm at 300 °C, ∼10–2 S/cm at 400 °C, and ∼10–1 S/cm at 500 °C. Analysis of X-ray and neutron diffraction data revealed that the materials possess a major rhombohedral (R3m) and a minor cubic (I23) phase. The R3m phase is similar to a fluorite-type superstructure with 3 × 3 × 3 subcells, and the I23 phase is equivalent to the known γ-Bi2O3 phase. The results of the Bi L3-edge X-ray absorption fine structure study show that the Bi local structure is heavily disordered, favoring oxide-ion conduction in both materials. Soft bond valence sum analysis of neutron powder diffraction data uncovers the pathways of the ionic conduction of the R3m and I23 phases. Our results of as-sintered (unaged), 400 °C/100 h, and 600 °C/100 h annealed (aged) samples of BSV0.087O and BCV0.087O demonstrate the long-term stability of phase, structure, and conduction properties. High conductivity at low temperatures and long-term stability of both materials make them potential candidates for low-temperature solid oxide fuel cells, oxygen pumps and sensors, and gas separation membrane applications.