Hydride Ion Conduction in Oxyhydride Thin Films

Oxyhydride thin films represent a burgeoning class of mixed-anion materials in which hydride (H–) and oxide (O2–) anions coexist within a crystalline or amorphous matrix. The incorporation of hydride ions into perovskite, rock-salt or layered frameworks yields a flexible anion sublattice that can support high rates of H– migration. Hydride-ion conduction in these films is governed by the availability of interstitial or vacancy sites, the energy landscape of anion hops and the polarizability of the lattice. Oxygen substitution or doping often enhances the pre-exponential term in the Arrhenius relation, leading to record conductivities at intermediate temperatures. Thin-film architectures afford precise control of composition, strain and defect distributions via techniques such as pulsed-laser deposition or reactive sputtering. The resulting materials display a rich interplay between ionic transport, electronic conductivity and lattice dynamics. Practical applications span solid-state hydrogen sensors, electrochemical reactors, all-solid-state batteries and switchable optical devices. Continued progress hinges on tailoring the anion ordering, film microstructure and interface chemistry to optimise hydride mobility while maintaining chemical stability under operating conditions.

Research from Nature Portfolio

Recent studies have demonstrated that oxygen-doped lanthanum hydride films exhibit exceptionally fast H– conduction with ionic conductivities exceeding 10–2 S cm–1 at intermediate temperatures. By tuning the oxygen content in LaH3−2xOx, researchers achieved a record combination of moderate activation energy and extraordinarily large pre-exponential factors, attributed to temperature-dependent enthalpy changes arising from H– interactions with La–O bonds. The dense hydride sublattice and high polarizability of H– underpin the strong temperature dependence of the conduction process. These findings establish a clear strategy for maximising hydride mobility via controlled anion substitution while preserving the favourable lattice framework of rare-earth hydrides.

Hydride Ion Conduction in Oxyhydride Thin Films publication trend

The graph below shows the total number of articles in hydride ion conduction in oxyhydride thin films across all publications each year (not limited to Nature Index journals).

Technical terms

Oxyhydride thin film: A solid layer in which oxide and hydride anions share a host lattice, prepared with thicknesses typically below one micrometre.

Hydride ion conduction: The transport of H– anions through a solid via hopping between lattice sites under an applied field or chemical gradient.

Activation energy: The energy barrier that must be overcome for an ion to move from one lattice site to another.

Pre-exponential factor: A term in the Arrhenius equation reflecting the intrinsic attempt frequency of ion hops independent of temperature.

Polaron: A quasiparticle comprising a charge carrier (electron or hole) coupled to the surrounding lattice distortion.

Band conduction: Charge transport occurring through delocalised electronic states extending across the material’s conduction band.

References

1. Characteristic fast H− ion conduction in oxygen-substituted lanthanum hydride. Nature Communications (2019).
2. Large Polaron Conduction, Photoconductivity, and Photochromism in GdOxH3−2x Oxyhydride Thin Films. Advanced Optical Materials (2023).
3. Band vs. polaron: vibrational motion and chemical expansion of hydride ions as signatures for the electronic character in oxyhydride barium titanate. Journal of Materials Chemistry A (2019).