A two-dimensional type I superionic conductor.

TitleA two-dimensional type I superionic conductor.
Publication TypeJournal Article
Year of Publication2021
AuthorsAJE Rettie, J Ding, X Zhou, MJ Johnson, CD Malliakas, NC Osti, DY Chung, R Osborn, O Delaire, S Rosenkranz, and MG Kanatzidis
JournalNature Materials
Start Page1683
Pagination1683 - 1688
Date Published12/2021

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, Ag<sub>2</sub>Se 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-KAg<sub>3</sub>Se<sub>2</sub>, by scattering techniques and complementary simulations. Quasi-elastic neutron scattering and ab initio molecular dynamics simulations confirm that the superionic Ag<sup>+</sup> 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.

Short TitleNature Materials