Layered monoclinic perrierite oxo-silicate La₄Mn₅Si₄O_22+δ: a new family of interstitial oxide ion conductor

Oxide-ion conductors are important for various energy applications such as solid oxide fuel cells, solid oxide electrolyser cells, etc [1]. State-of-the-art stable oxygen active materials often have adequate oxygen ion diffusion and chemical surface exchange only at high temperatures (> 700 ^oC). A promising strategy to improve the oxygen ion transport is to use interstitial oxygen ion conductors as the interstitial hop barriers are often lower than vacancy mediated hops, potentially enabling reduced operation temperatures. However, due to the large size of the oxide ion, the formation of an adequate concentration of interstitials is difficult and hence the number of interstitial oxygen conductors is currently limited to just a handful of compounds, e.g., Ruddlesden-Popper, apatite, and disordered hexagonal perovskites [2-3].

In this work we developed an integrated computational and experimental approach to discover new interstitial oxygen diffusers which might show efficient oxygen transport at low temperature. High-throughput computational screening of the 33,975 oxide materials from the Materials Project revealed the easy formation of interstitial oxygen (ab initio predicted formation energy ~ -0.11 eV at 25 ^oC in air) and high oxide ion diffusivity in a new class of material La₄Mn₅Si₄O_22+δ (LMSO), motivating us to synthesize and study its oxide ion transport properties. Electron probe micro-analyser and iodometric titration revealed the presence of the hyper stoichiometric oxygen (δ ~ + 0.5) in LMSO lattice, consistent with the computational results. Electrical conductivity relaxation study also demonstrated promising self-diffusion and surface exchange coefficients of oxygen ion over the temperature range from 600 to 750 ^oC.

In conclusion, this study introduces layered perrierite LMSO as a new class of interstitial oxide ion conductors and the overall approach may help the rational design of oxide ion conductors-based devices suitable for efficient and stable applications at low temperature.

References:

[1] M. Coduri, M. Karlsson, L. Malavasi, J. Mater. Chem. A 10 (2022) 5082-5110.

[2] S. Xu, R. Jacobs, D. Morgan, Chem. Mater. 30 (2018) 7166-7177.

[3] M. Yashima, et al., Nat. Com. 12 (2021) 556.