Bond-Switching Reconstruction in Bare Ti3C2 MXene

Abstract

MXene properties are typically tuned through composition, surface termination, and intercalation, while the metal-carbon framework topology is considered fixed. Here, we demonstrate that this framework can reconstruct. Unconstrained relaxations of biaxially strained bare Ti3C2 yield a dynamically stable polymorph, N, featuring a 15-atom primitive cell, six distinct Ti-C bond classes, and 2.55 {\AA} Ti-Ti pairs. The coherent transformation pathway crosses an 8.47 eV barrier per cell but first reaches another reconstructed minimum, N', lying 1.08 eV below N, revealing a family of bond-switched networks. Phase N lies 7.58 eV per cell above the parent. Reverse barriers along the calculated pathway are 1.50 and 1.98 eV per cell for N and N', respectively. Reconstruction quenches the parent spin polarization, yielding a nonmagnetic metal with a nearly fourfold increase in Fermi-level density of states. Bader and electron-localization analyses suggest charge redistribution from C toward Ti associated with Ti-Ti pairing. In multilayers, reconstructed layers form interlayer Ti-C bonds. A 10% biaxial tension halves the phase-energy difference, and pressure reverses phase ordering near 85 GPa. These results establish bond-switching reconstruction as a mechanically controllable structural degree of freedom in MXenes.