High Oxygen Ion Conductivity in Hexagonal Perovskite Ba<sub>7</sub>Nb<sub>4</sub>MoO<sub>20</sub> via Epitaxy-Assisted Orienting of Two-Dimensional Diffusion Pathways.
basic_science · Level V
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- Record sourced from PubMed, PMID 40960812.
- Also identified by DOI 10.1021/acsnano.5c09279.
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Abstract
Oxygen ion conductors are a key component in solid-state ionic devices such as fuel cells, catalysts, sensors, and artificial intelligent devices. The recent discovery of undoped Ba<sub>7</sub>Nb<sub>4</sub>MoO<sub>20</sub> hexagonal perovskites has attracted great attention due to the existence of two-dimensional oxygen diffusion pathways between NbO<sub>4</sub> and MoO<sub>4</sub> tetrahedra. However, there have been rare studies on the control parameters for hexagonal perovskites to further boost oxygen ion transport at lower temperatures. Here, we find significantly higher oxygen ion conductivity (5.6 × 10<sup>-4</sup> S cm<sup>-1</sup> at 340 °C, 3.2 × 10<sup>-1</sup> S cm<sup>-1</sup> at 600 °C) of (001)-oriented Ba<sub>7</sub>Nb<sub>4</sub>MoO<sub>20</sub> epitaxial films by several orders of magnitude than that of sintered pellets. Our report is comparable to the oxygen ion conductivities of conventional doped conductors. X-ray diffraction and atomic-scale characterization with energy-dispersive X-ray spectroscopy reveal that this epitaxy-driven enhancement is attributed to the good alignment of two-dimensional pathways in an ion current direction. Our design principle of hexagonal perovskites will trigger an advanced understanding of the correlation between the crystal structure and ultrahigh oxygen ion conductivity.