Issue 43, 2024

The role of vanadium substitution in the oxygen sublattice disorder of Ba7Nb4MoO20-based hexagonal perovskite oxide-ion conductors

Abstract

Ba7Nb4MoO20-based hexagonal perovskite derivatives are promising oxygen-ion conductors for solid electrolytes in solid-oxide fuel cells and electrolysers. A thorough understanding of chemical substitution and its impact on structural features conducive to high ionic conductivity is fundamental for decreasing the operation temperature of such devices. Here, a new 7H polytype-based composition, namely Ba7Nb3.9−xVxMo1.1O20.05, is investigated to assess the effect of vanadium substitution. Structural changes upon V incorporation are studied using X-ray and neutron diffraction, as well as 51V and 93Nb solid-state nuclear magnetic resonance spectroscopy. For the undoped composition at room temperature, two distinct oxygen sites (O1 and O5) are found along the palmierite-like layer, corresponding to a mix of four- and six-fold coordination for adjacent M2 cations. At high temperature (527 °C), reorganization of oxygen results in the major occupation of O1 and four-fold (tetrahedral) coordination of the M2 cations. The same rearrangement is observed upon V-substitution, but already at room temperature. From 51V NMR, we identified a tetrahedral coordination for V5+ cations, indicating their preferential occupation of the M2 site. This preferential occupation by V5+ cations is correlated with increasing tetrahedral coordination of Nb5+ cations as observed from 93Nb NMR. Altogether, these observations indicate that V-substitution impacts the oxygen sublattice so as to mimic the high-temperature structure. Additionally, BVSE calculations demonstrate a decreasing energy barrier for O2− migration associated with the presence of vanadium in the structure. This conclusion corroborates the hypothesis that vanadium's propensity for a lower coordination number is beneficial for promoting high O2− mobility in this promising class of oxide-ion conductors.

Graphical abstract: The role of vanadium substitution in the oxygen sublattice disorder of Ba7Nb4MoO20-based hexagonal perovskite oxide-ion conductors

Supplementary files

Article information

Article type
Paper
Submitted
05 Mar 2024
Accepted
24 Sep 2024
First published
25 Sep 2024
This article is Open Access
Creative Commons BY license

J. Mater. Chem. A, 2024,12, 30082-30095

The role of vanadium substitution in the oxygen sublattice disorder of Ba7Nb4MoO20-based hexagonal perovskite oxide-ion conductors

A. O. Biffo, T. Famprikis and P. B. Groszewicz, J. Mater. Chem. A, 2024, 12, 30082 DOI: 10.1039/D4TA01540A

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