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A two-dimensional type I superionic conductor


Superionic conductors possess liquid-like ionic diffusivity in the solid state, finding wide applicability from electrolytes in energy storage to materials for thermoelectric energy conversion. Type I superionic conductors (for example, AgI, Ag2Se and so on) are defined by a first-order transition to the superionic state and have so far been found exclusively in three-dimensional crystal structures. Here, we reveal a two-dimensional type I superionic conductor, α-KAg3Se2, by scattering techniques and complementary simulations. Quasi-elastic neutron scattering and ab initio molecular dynamics simulations confirm that the superionic Ag+ ions are confined to subnanometre sheets, with the simulated local structure validated by experimental X-ray powder pair-distribution-function analysis. Finally, we demonstrate that the phase transition temperature can be controlled by chemical substitution of the alkali metal ions that compose the immobile charge-balancing layers. Our work thus extends the known classes of superionic conductors and will facilitate the design of new materials with tailored ionic conductivities and phase transitions.

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Fig. 1: QENS of KAg3Se2.
Fig. 2: Molecular dynamics simulations and structural comparison.
Fig. 3: Local structure analysis.
Fig. 4: Effects of cation substitution.

Data availability

Data that support the plots within this paper and other findings of this study are available from the corresponding authors upon reasonable request. Source data are provided with this paper.


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We are indebted to W. Xu for assistance in the acquisition and analysis of X-ray total scattering data and to E. Mamontov for valuable discussions concerning the QENS data analysis. M.J.J. acknowledges HORIBA-Motor Industry Research Association (MIRA), University College London (UCL) and the Engineering and Physical Sciences Research Council (EPSRC) (EP/R513143/1) for a Collaborative Awards in Science and Engineering (CASE) studentship. This work was performed primarily at the Materials Science Division at Argonne National Laboratory, supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division. We gratefully acknowledge the computing resources provided on Bebop, the high-performance computing clusters operated by the Laboratory Computing Resource Center at Argonne National Laboratory. First-principles modelling at Duke University (J.D., O.D.) was supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, under award no. DE-SC0019299. Work at Oak Ridge National Laboratory’s Spallation Neutron Source is supported by the US Department of Energy, Office of Basic Energy Sciences. The Oak Ridge National Laboratory is managed by UT–Battelle for the US Department of Energy under contract no. DEAC05-00OR22725. This work made use of the Integrated Molecular Structure Education and Research Center (IMSERC) facility at Northwestern University, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-2025633) and Northwestern University. A.J.E.R. and M.J.J. gratefully acknowledge the Faraday Institution Lithium-Sulfur Technology Accelerator (LiSTAR) programme (FIRG014, EP/S003053/1) for funding.

Author information




A.J.E.R., S.R. and M.G.K. conceived the study. A.J.E.R., X.Z. and D.Y.C. synthesized and characterized all materials. A.J.E.R., R.O. and N.C.O. acquired and analysed the neutron scattering data. J.D. and O.D. performed the AIMD simulations. M.J.J. and C.D.M. conducted the PDF analysis and structural modelling. The manuscript was mainly written and revised by A.J.E.R., S.R. and M.G.K. All authors approved the final version of the manuscript.

Corresponding authors

Correspondence to Alexander J. E. Rettie or Stephan Rosenkranz or Mercouri G. Kanatzidis.

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The authors declare no competing interests.

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Peer review information Nature Materials thanks Stefan Adams, Tom Nilges and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–18 and Discussion.

Supplementary Video 1

Animation of molecular dynamics simulations of α-KAg3Se2 at 800 K.

Source data

Source Data Fig. 1

Source data for graphs in Fig. 1.

Source Data Fig. 2

Source data for graphs in Fig. 2.

Source Data Fig. 3

Source data for graphs in Fig. 3.

Source Data Fig. 4

Source data for graphs in Fig. 4.

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Rettie, A.J.E., Ding, J., Zhou, X. et al. A two-dimensional type I superionic conductor. Nat. Mater. (2021).

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