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

Abstract

Herein, highly stable and exceptionally high oxideion conducting vanadium-and strontium/calcium-codoped bismuth oxides of Bi 0.893 Sr 0.02 V 0.087 O 1.577 (BSV 0.087 O) and Bi 0.893 Ca 0.02 V 0.087 O 1.577 (BCV 0.087 O) 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 Xray 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-Bi 2 O 3 phase. The results of the Bi L 3 -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 BSV 0.087 O and BCV 0.087 O demonstrate the longterm 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.