Interstitial Oxygen and a Two-Dimensional Migration Pathway in Mo-Substituted Palmierite Ba 3 V 2−x Mo x O 8+x/2
Year: 2026
Type: preprint
Abstract: Palmierite oxides are promising oxide-ion conductors, with conductivities exceeding those of related hexagonal perovskite derivatives. However, aliovalent Mo6+ substitution in Ba 3 V 2 O 8 has previously been demonstrated only at high substitution levels. Here, the Ba 3 V 2-x Mo x O 8+x/2 series (0 ≤ x ≤ 0.3) was investigated using X-ray and neutron powder diffraction, 51 V and 17 O solid-state NMR spectroscopy combined with density functional theory (DFT), and bond-valence site-energy (BVSE) calculations. Combined Rietveld refinement reveals that Mo6+ substitution introduces a charge-compensating interstitial oxygen site (O3) at x = 0.3, transforming isolated (V, Mo)O 4 tetrahedra into corner-sharing polyhedra with mixed coordination. DFT-supported 17 O NMR identifies additional oxygen environments associated with Mo in four- and five-fold coordination, suggesting oxygen bridges between adjacent MoO5 polyhedra. 51 V NMR confirms predominantly tetrahedral vanadium coordination, alongside a minority V environment , distorted by occupation of a nearby O3 site. BVSE calculations indicate that O3 bridges neighboring polyhedra in the abplane, enabling a low-barrier, two-dimensional oxide-ion migration pathway involving apical O1 and interstitial O3 sites. These findings establish interstitial oxygen incorporation as the key structural mechanism facilitating low-barrier two-dimensional oxide-ion transport at low Mo substitution levels in the palmierite family, with broader implications for hexagonal perovskite ionic conductors.
Source: ChemRxiv
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7223187038