Liquid-like cationic sub-lattice in copper selenide clusters

• Published in: Nature communications Vol. 8; no. 1; p. 14514
• Main Authors: White, Sarah L., Banerjee, Progna, Jain, Prashant K.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 20-02-2017; Nature Publishing Group; Nature Portfolio
• Subjects: 140/133; 639/301/299; 639/301/357; Copper; Electrolytes; Fuel cells; Humanities and Social Sciences; multidisciplinary; Nanocrystals; Phase transitions; Science; Science (multidisciplinary); Temperature; United States > US; Illinois
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms14514

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 Cu
2
Se clusters make them suitable as fast electro-optic switches.
Copper selenide is super-ionic only at high temperatures. Here, the authors discover room temperature super-ionic behaviour in ultrasmall clusters of Cu
2
Se—but not in its larger or bulk forms—owing to an unusual liquid-like cationic sub-lattice, in which octahedral sites are stabilized by size-dependent compressive strain.