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Discovery of a Two-Dimensional Type I Superionic Conductor

preprint
revised on 24.08.2020, 08:30 and posted on 24.08.2020, 08:55 by Alex Rettie, Jingxuan Ding, Michael Johnson, Christos Malliakas, Naresh Osti, Duck Young Chung, Raymond Osborn, Olivier Delaire, Stephan Rosenkranz, Mercouri Kanatzidis

Type I superionic conductors (e.g., AgI, Ag2Se, etc.) are defined by an abrupt transition to the superionic state and have so far been found exclusively in 3D crystal structures. Here, we reveal a new 2D type I superionic conductor, α-KAg3Se2 by total scattering techniques and complementary simulations. Quasi-elastic neutron scattering (QENS) from the high temperature superionic phase match a simple Fickian diffusion mechanism with a diffusion coefficient of ~10-5 cm2 s-1 between 710 and 740 K. Ab initio molecular dynamics simulations confirm that the mobile Ag+ ions are confined to 4 Å thick layers, in addition to reproducing the experimental diffusion coefficient from QENS and the local structure obtained from X-ray powder pair-distribution-function analysis. Finally, chemical substitutions suggest that the nature of alkali metal ions comprising the charge-balancing layers can facilitate or inhibit the phase transition temperature.

History

Email Address of Submitting Author

a.rettie@ucl.ac.uk

Institution

University College London

Country

United Kingdom

ORCID For Submitting Author

0000-0002-2482-9732

Declaration of Conflict of Interest

None

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