title: Liquid-like cationic sub-lattice in copper selenide clusters.
abstract: Super-ionic solids, which exhibit ion mobilities as high as those in liquids or molten salts, have been employed as solid-state electrolytes in batteries, improved thermoelectrics and fast-ion conductors in super-capacitors and fuel cells. Fast-ion transport in many of these solids is supported by a disordered, 'liquid-like' sub-lattice of cations mobile within a rigid anionic sub-lattice, often achieved at high temperatures or pressures via a phase transition. Here we show that ultrasmall clusters of copper selenide exhibit a disordered cationic sub-lattice under ambient conditions unlike larger nanocrystals, where Cu+ions and vacancies form an ordered super-structure similar to the bulk solid. The clusters exhibit an unusual cationic sub-lattice arrangement wherein octahedral sites, which serve as bridges for cation migration, are stabilized by compressive strain. The room-temperature liquid-like nature of the Cu+sub-lattice combined with the actively tunable plasmonic properties of the Cu2Se clusters make them suitable as fast electro-optic switches.
authors.affiliation: Department of Chemistry, University of Illinois at Urbana-Champaign, CLSL A, 601 South Goodwin Avenue, Urbana, Illinois 61801, USA.
authors.forename: Sarah L
authors.initials: SL
authors.lastname: White
authors.affiliation: Department of Physics, University of Illinois at Urbana-Champaign, Loomis Laboratory, 1110 West Green Street, Urbana, Illinois 61801, USA.
authors.forename: Progna
authors.initials: P
authors.lastname: Banerjee
authors.affiliation: Department of Chemistry, University of Illinois at Urbana-Champaign, CLSL A, 601 South Goodwin Avenue, Urbana, Illinois 61801, USA.|Department of Physics, University of Illinois at Urbana-Champaign, Loomis Laboratory, 1110 West Green Street, Urbana, Illinois 61801, USA.
authors.forename: Prashant K
authors.identifier: 0000-0002-7306-3972
authors.initials: PK
authors.lastname: Jain