High-Dielectric 2D Bismuth Oxides with Large Bandgaps: The Role of 6s2 Lone Pair Hybridization

Large-bandgap and high-dielectric 2D dielectrics are crucial for transistor performance because they maximize gate-to-channel capacitive coupling, yet such high-quality materials remain scarce. This study employed first-principles calculations to predict 18 distinct 2D bismuth oxides (BiOs). It is demonstrated that the 6s2 lone pairs in 2D BiOs form benign positive feedback between the bandgap and dielectric constant. The hybridization of 6s2 and 6pz orbitals is key to setting the bandgap, revealing a significant negative linear relationship between the bond length and energy gap. In particular, due to the stereochemical activity of 6s2 that enhances the ionic contribution, these materials are capable of sustaining a high dielectric constant value surpassing 24, even within bandgaps wider than 4 eV. This discovery enhances the theoretical understanding of 2D materials exhibiting large bandgaps and high dielectric constants, providing deeper insights into the impact of lone pairs on 2D materials.