High oxide-ion conductivity through the interstitial oxygen site in Ba<sub>7</sub>Nb<sub>4</sub>MoO<sub>20</sub>-based hexagonal perovskite related oxides.
basic_science · Level V
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- Record sourced from PubMed, PMID 33495469.
- Also identified by DOI 10.1038/s41467-020-20859-w and PMC identifier 7835212.
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Abstract
Oxide-ion conductors are important in various applications such as solid-oxide fuel cells. Although zirconia-based materials are widely utilized, there remains a strong motivation to discover electrolyte materials with higher conductivity that lowers the working temperature of fuel cells, reducing cost. Oxide-ion conductors with hexagonal perovskite related structures are rare. Herein, we report oxide-ion conductors based on a hexagonal perovskite-related oxide Ba<sub>7</sub>Nb<sub>4</sub>MoO<sub>20</sub>. Ba<sub>7</sub>Nb<sub>3.9</sub>Mo<sub>1.1</sub>O<sub>20.05</sub> shows a wide stability range and predominantly oxide-ion conduction in an oxygen partial pressure range from 2 × 10<sup>-26</sup> to 1 atm at 600 °C. Surprisingly, bulk conductivity of Ba<sub>7</sub>Nb<sub>3.9</sub>Mo<sub>1.1</sub>O<sub>20.05</sub>, 5.8 × 10<sup>-4</sup> S cm<sup>-1</sup>, is remarkably high at 310 °C, and higher than Bi<sub>2</sub>O<sub>3</sub>- and zirconia-based materials. The high conductivity of Ba<sub>7</sub>Nb<sub>3.9</sub>Mo<sub>1.1</sub>O<sub>20.05</sub> is attributable to the interstitial-O5 oxygen site, providing two-dimensional oxide-ion O1-O5 interstitialcy diffusion through lattice-O1 and interstitial-O5 sites in the oxygen-deficient layer, and low activation energy for oxide-ion conductivity. Present findings demonstrate the ability of hexagonal perovskite related oxides as superior oxide-ion conductors.