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Synthesis and Electronic Structure of a 3D Crystalline Stack of MXene-Like Sheets

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journal contribution
posted on 21.11.2019, 20:34 by Daniel L. Druffel, Matthew G. Lanetti, Jack D. Sundberg, Jacob T. Pawlik, Madeline S. Stark, Carrie L. Donley, Lauren M. McRae, Katie M. Scott, Scott C. Warren
Despite the interest in MXenes in the past decade, MXenes are often highly disordered, which can complicate their study and use. For example, nearly all MXenes have a random mixture of surface terminations (−O, −OH, −F). In addition, restacked 3D films have turbostratic disorder and often contain ions, solvent, and other species in between their layers. Here, we report Y2CF2, a layered crystal with a unit cell isostructural to a MXene, in which layers are capped only by fluoride anions. We directly synthesize the 3D crystal through a high-temperature solid-state reaction, which affords the 3D crystal in high yield and purity and ensures that only fluoride ions terminate the layers. We characterize the crystal structure and electronic properties using a combination of experimental and computational techniques. We find that relatively strong electrostatic interactions bind the layers together into a 3D crystal and further find that the lack of orbital overlap between layers gives rise to a description of Y2CF2 as slabs of MXene-like sheets electrically insulated from one another. Therefore, we consider Y2CF2 as a pure 3D crystalline stack of MXene-like sheets. In addition, Y2CF2 is the first transition metal carbide fluoride experimentally synthesized. We hope this work inspires further exploration of transition metal carbide fluorides, which are potentially a large and useful class of compositions.

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