Enhanced Phase\nStability and Oxide-Ion Conductivity\nin V- and Sr/Ca-Codoped Bi<sub>2</sub>O<sub>3</sub> Ceramics

Herein, highly stable and exceptionally high oxide-ion\nconducting\nvanadium- and strontium/calcium-codoped bismuth oxides of Bi<sub>0.893</sub>Sr<sub>0.02</sub>V<sub>0.087</sub>O<sub>1.577</sub> (BSV<sub>0.087</sub>O) and Bi<sub>0.893</sub>Ca<sub>0.02</sub>V<sub>0.087</sub>O<sub>1.577</sub> (BCV<sub>0.087</sub>O) have been reported. Both materials\nexhibit conductivity values of ∼10<sup>–3</sup> S/cm\nat 300 °C, ∼10<sup>–2</sup> S/cm at 400 °C,\nand ∼10<sup>–1</sup> S/cm at 500 °C. Analysis of\nX-ray and neutron diffraction data revealed that the materials possess\na major rhombohedral (<i>R</i>3<i>m</i>) and a\nminor cubic (<i>I</i>23) phase. The <i>R</i>3<i>m</i> phase is similar to a fluorite-type superstructure with\n3 × 3 × 3 subcells, and the <i>I</i>23 phase is\nequivalent to the known γ-Bi<sub>2</sub>O<sub>3</sub> phase.\nThe results of the Bi L<sub>3</sub>-edge X-ray absorption fine structure\nstudy show that the Bi local structure is heavily disordered, favoring\noxide-ion conduction in both materials. Soft bond valence sum analysis\nof neutron powder diffraction data uncovers the pathways of the ionic\nconduction of the <i>R</i>3<i>m</i> and <i>I</i>23 phases. Our results of as-sintered (unaged), 400 °C/100\nh, and 600 °C/100 h annealed (aged) samples of BSV<sub>0.087</sub>O and BCV<sub>0.087</sub>O demonstrate the long-term stability of\nphase, structure, and conduction properties. High conductivity at\nlow temperatures and long-term stability of both materials make them\npotential candidates for low-temperature solid oxide fuel cells, oxygen\npumps and sensors, and gas separation membrane applications.