Superatomic crystals are three-dimensional periodic arrays in which preformed sub-nanometer molecular clusters, which we term superatoms, emulate the role of atoms in traditional solid-state compounds. In the search for rationally-assembled functional materials, superatomic crystals have emerged as a unique class of compounds that combine programmable nanoscale building blocks and atomic precision. As such, they bridge traditional semiconductors, molecular solids, and nanocrystal arrays by combining their most attractive features. In this presentation, I will describe a superatomic crystal that features two separate structural phase transitions. This material is formed by the assembly of the cluster Co6Te8(PEt3)6 and C70 fullerene into an ionic structure containing both monomeric and dimerized fullerenes. This crystal exhibits a coupled structural-electronic phase transition at high temperature caused by the homolytic cleavage of C1402– dimers. I will discuss how this transition triggers the emergence of a new electronic band in the fullerene sublattice, and transforms the electrical transport properties of the material. Independently, at low temperature the lattice undergoes an order-disorder transition that transforms the thermal transport properties of the material, from a phonon glass to a phonon crystal. By deciphering the underlying structural and electronic processes, we reveal how superatomic crystals differ radically from other types of superlattices, which themselves are too disordered to exhibit such extraordinary critical phenomena.

Switchable transport behaviors in a phase change superatomic crystal

2019 Fall National Meeting

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