Synthesis and Electronic Structure of a Crystalline Stack of MXene Sheets

TL;DR

This paper reports the synthesis and characterization of Y2CF2, a 3D crystalline stack of MXene-like sheets with fluoride terminations, providing insights into its structure and electronic properties, and introducing the first transition metal carbide fluoride.

Contribution

The study presents the first synthesis of a transition metal carbide fluoride, Y2CF2, as a pure 3D crystal with MXene-like layers capped solely by fluoride ions, advancing material understanding.

Findings

Y2CF2 is a 3D crystal with MXene-like layers.

Layers are bound by electrostatic interactions, not orbital overlap.

Y2CF2 is the first transition metal carbide fluoride synthesized.

Abstract

Despite the interest in MXenes in the last decade, all of the MXenes reported have a random mixture of surface terminations (-O, -OH, -F). In addition, restacked 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 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.