Impact of Composition on the Structural, Electronic, and Mechanical Properties of M3C2T2 MXenes

Abstract

MXenes are a family of layered 2D materials useful for a wide variety of applications. Their properties can be fine-tuned by choice of chemical composition (metal and termination), but the vast majority of published studies have focused on Ti-based MXenes with -O, -F, and -OH terminations. Furthermore, MXenes may have ABC or ABA stacking, but typical density functional theory (DFT) studies assume only ABC stacking. Thus, most modeling papers of MXenes have focused only on specific targeted MXenes. In this work we aimed to provide a comprehensive DFT study of possible MXenes in order to motivate and characterize MXenes beyond those common in the literature. We modeled 99 different M₃C₂T₂ MXenes (including groups 4, 5, and 6 metals; also including halogen, chalcogen, -OH, and -NH terminations). We made no assumptions about preferred termination site or stacking symmetry of these MXenes. 20% of the studied MXenes were found to prefer ABA stacking. In total we performed more than 2,000 DFT calculations to predict the structural, electronic, and mechanical properties of these MXenes. We identified several MXenes with exceptional properties, and identified potential applications of such MXenes. We also connected the termination/metal choice to trends in their properties. Our work highlights how different properties of MXenes can be tuned based on their composition, and thus motivates further work on these materials.