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Discovery of a Two-Dimensional Type I Superionic Conductor

revised on 24.08.2020 and posted on 24.08.2020 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.


Email Address of Submitting Author


University College London


United Kingdom

ORCID For Submitting Author


Declaration of Conflict of Interest