Computational discovery of layered Sc-based MOenes (Sc2OX2, X = Cl, Br, I): Insights into the electronic and thermal transport properties

The discovery of novel materials through first-principles calculations is an exciting and rapidly advancing frontier in materials science. In this study, we predict three novel layered Sc-based MOenes (Sc₂OCl₂, Sc₂OBr₂, and Sc₂OI₂), employing a variable-composition evolutionary algorithm combined with the first-principles calculations. The predicted bulk materials are thermodynamically and thermally stable. We have also examined the cleavage energy and the electronic and phonon dispersions of the monolayers. Our cleavage energy calculations indicate easy exfoliation of monolayers from their bulk counterparts. Monolayer Sc₂OCl₂ and Sc₂OBr₂ demonstrate dynamic stability, while monolayer Sc₂OI₂ shows instability at the X high symmetry point. Our calculations show that bulk Sc₂OX₂ are semiconductors with a band gap ranging from 0.51 eV (Sc₂OCl₂) to 0.59 eV (Sc₂OI₂). A slight increase in the band gap is observed for the monolayers of Sc₂OBr₂ and Sc₂OI₂. Our findings reveal that at a n-type doping concentration of 2×10²¹ cm⁻³, bulk Sc₂OCl₂ has a room temperature electrical conductivity of 4.87×10⁵ Sm⁻¹, followed by bulk Sc₂OBr₂ (3.64×10⁵ Sm⁻¹) and bulk Sc₂OI₂ (4.89×10⁵ Sm ⁻¹). The bulk Sc₂OCl₂ halide demonstrate room temperature lattice thermal conductivity of 8.7 Wm⁻¹K⁻¹, significantly surpassing bulk Sc₂OBr₂ (4.6 Wm⁻¹K⁻¹) and bulk Sc₂OI₂ (2.8 Wm⁻¹K⁻¹). These results highlight the crucial role of halogen atomic mass in governing thermal transport. We present these moderate to lightweight Sc-based MOenes compounds as promising candidates for further computational and experimental investigations, with the potential to uncover new physics in materials.