Tuning structure and properties of Ti₂B₂T_x MBenes via halogen terminations

MBenes are a relatively new family of two-dimensional (2D) transition metal borides that can be synthesized through selective etching of A-layers from MAB phases. As in MXenes, surface termination is a key factor influencing their properties. Inspired by the recent discovery of Ti₂B₂T_x MBene, this Density Functional Theory (DFT) study investigates halogen-terminated Ti₂B₂T_x compounds (T_x = Cl, Br, and I) with coverages ranging from 100% (ideal, x = 2) to 50% (x = 1), for which the unoccupied sites are either treated as vacancies or filled with oxygen atoms. Our main findings reveal that oxygen incorporation is favorable for all halogen terminations, and the interlayer binding energies of the multilayer-Ti₂B₂T_x MBenes are comparable to those of other vdW 2D materials. Further, the MBenes exhibit good mechanical properties and low interlayer sliding energy barriers, suggesting suitability for tribological applications. The effect of the surface termination on the electronic structures and adsorption energies was also investigated for fundamental insights. Finally, the calculated work function ranges from ~3 to 5 eV, indicating that it can be tuned with precise control over termination coverage and composition, offering a powerful route to tailoring MBene properties for improved application-specific performance.