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Photo-enhanced ionic conductivity across grain boundaries in polycrystalline ceramics

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Abstract

Grain boundary conductivity limitations are ubiquitous in material science. We show that illumination with above-bandgap light can decrease the grain boundary resistance in solid ionic conductors. Specifically, we demonstrate the increase of the grain boundary conductance of a 3 mol% Gd-doped ceria thin film by a factor of approximately 3.5 at 250 °C and the reduction of its activation energy from 1.12 to 0.68 eV under illumination, while light-induced heating and electronic conductivity could be excluded as potential sources for the observed opto-ionic effect. The presented model predicts that photo-generated electrons decrease the potential barrier heights associated with space charge zones depleted in charge carriers between adjacent grains. The discovered opto-ionic effect could pave the way for the development of new electrochemical storage and conversion technologies operating at lower temperatures and/or higher efficiencies and could be further used for fast and contactless control or diagnosis of ionic conduction in polycrystalline solids.

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Fig. 1: General grain boundary characteristics and the impact of UV illumination.
Fig. 2: Temperature dependance of the opto-ionic effect.
Fig. 3: SFITs in light and dark phases.
Fig. 4: Frequency-dependent optical modulation of resistance response by IMPS.
Fig. 5: Suggested mechanism of the opto-ionic effect and the consequences for potential distribution and charge carrier concentrations.

Data availability

Source data are provided with this paper. Source data for Figs. 1–4 and Supplementary Figs. 9–11 are available from the online data repository Figshare with identifier https://doi.org/10.6084/m9.figshare.c.5707109.v4. Remaining data that support the findings of this study are available from the corresponding authors upon reasonable request.

Change history

  • 03 March 2022

    In the version of this article initially published, the address for IREC was imprecisely written and has now been updated in the HTML and PDF versions of the article.

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Acknowledgements

We thank G. F. Harrington for the valuable input on sample preparation and characterization and K. May for help with the atomic force microscopy measurements. T.D. and H.L.T. acknowledge support for their research from the US Department of Energy, Basic Energy Sciences under award number DE-SC0002633 (Chemomechanics of Far-From-Equilibrium Interfaces). D.K. acknowledges support by the Japan Society for the Promotion of Science Core-to-Core Program, A. Advanced Research Networks: ‘Solid Oxide Interfaces for Faster Ion Transport’, as well as funding from the Kakenhi Grant-In-Aid for young scientists, grant numbers 18K13993 and 20K15028. D.K. and H.L.T. appreciate preliminary discussions with H. Matsumoto of Kyushu University and T. Lippert and D. Pergolesi of the Paul Scherrer Institute. J.L.M.R., J.C.G.-R. and T.D. acknowledge the Swiss National Science Foundation for grant number BSSGI0_155986/1, and Equinor for grant Agr no. 4502981450. This work made use of the Materials Research Science and Engineering Center Shared Experimental Facilities at the Massachusetts Institute of Technology, supported by the National Science Foundation under award number DMR-14-19807. A portion of this work was performed at the Center for Nanoscale Systems, a member of the National Nanotechnology Coordinated Infrastructure Network, which was supported by the National Science Foundation under National Science Foundation award no. 1541959.

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Contributions

H.L.T. conceived the concept; T.D. and D.K. performed all experiments except the atomic force microscopy and scanning electron microscopy experiments, which were performed by J.C.G.-R.; H.L.T. and J.L.M.R. supervised the work. The manuscript was written by T.D., D.K., J.L.M.R. and H.L.T., and all authors contributed to discussions and editing.

Corresponding authors

Correspondence to Thomas Defferriere, Dino Klotz or Harry L. Tuller.

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Nature Materials thanks Koji Amezawa and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 Additional polycrystalline sample measured at low temperatures.

Arrhenius plot of additional sample A1. As guide, the measurements of the epitaxial and polycrystalline samples from the main text are also plotted as full lines in the same color code as in the main text (same Figure appears as Supplementary Fig. S9).

Source data

Supplementary information

Supplementary Information

Supplementary Sections 1–19, Figs. 1–24 and Tables 1–6.

Source data

Source Data Fig. 1

Unprocessed impedance data.

Source Data Fig. 2

Temperature-dependent conductivity (fits of data from Fig. 1).

Source Data Fig. 3

SFITs (unprocessed raw data over time).

Source Data Fig. 4

IMPS (measured raw data and fitted time constant).

Source Data Extended Data Fig. 1

Unprocessed impedance data gathered from additional sample A1.

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Defferriere, T., Klotz, D., Gonzalez-Rosillo, J.C. et al. Photo-enhanced ionic conductivity across grain boundaries in polycrystalline ceramics. Nat. Mater. 21, 438–444 (2022). https://doi.org/10.1038/s41563-021-01181-2

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