Enhanced Phase Stability and Oxide-Ion Conductivity in V- and Sr/Ca-Codoped Bi sub(2) O sub(3) Ceramics

Abstract

Herein, highly stable and exceptionally high oxide-ion conducting vanadium- and strontium/calcium-codoped bismuth oxides of Bi sub(0.893) Sr sub(0.02) V sub(0.087) O sub(1.577) (BSV sub(0.087) O) and Bi sub(0.893) Ca sub(0.02) V sub(0.087) O sub(1.577) (BCV sub(0.087)O) have been reported. Both materials exhibit conductivity values of approx. 10 sup(-3) S/cm at 300 degrees C, approx. 10 sup(-2) S/cm at 400 degrres C, and approx. 10 sup(-1) S/cm at 500 degrees 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 x 3 x 3 subcells, and the I23 phase is equivalent to the known Gamma-Bi sub(2) O sub(3) phase. The results of the Bi L sub(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 degrees C/100 h, and 600 degrees C/100 h annealed (aged) samples of BSV sub(0.087) O and BCV sub(0.087) O 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.