Stabilizing superconductivity of ternary metal pentahydride [Formula: see text] via electronic topological transitions under high pressure from first principles evolutionary algorithm

Realization of hydrogenation-induced superconductivity in two-dimensional Ti2N MXene

Two-dimensional (2D) MXene superconductors have been currently attracting considerable interest due to their unique electronic properties and diverse applicability. Utilizing first-principles computational methods, we have designed two distinct configurations of hydrogenated 2D Ti2N MXene materials, namely Ti2NH2 and Ti2NH4, and have conducted an exhaustive analysis of their structural stability, electronic characteristics, and superconductivity. Hydrogenation endows monolayer Ti2N with inherent metallic characteristics, as evidenced by an elevated density of states (DOS) at the Fermi level (Ef). Notably, Ti2NH4 exhibits a superconducting critical temperature (Tc) of 15.8 K, which is predominantly ascribed to the electronic contributions stemming from the Ti 3d orbitals. Analysis of phonon dispersion underscores the pivotal role that diverse lattice vibrational modes play in electron-phonon coupling (EPC), particularly the significance of low-frequency vibrations for facilitating electron pairing and the emergence of superconductivity. Furthermore, strain engineering can effectively modulate the superconducting properties of Ti2NH4, with a 2% tensile strain enhancing the EPC strength (λ) to 0.857 and increasing Tc to 18.7 K. This research elucidates the superconducting mechanisms of hydrogenated Ti2N structures, offering valuable insights for the development of novel 2D superconducting materials.

Hydrogen-induced phase stability and phonon mediated-superconductivity in two-dimensional van der Waals Ti2C MXene monolayer

Herein, we report the phase stability of the hydrogenated Ti₂C MXene monolayer using an evolutionary algorithm based on density functional theory. We predict the existence of hexagonal Ti₂CH, Ti₂CH₂, and Ti₂CH₄. The dynamic and energetic stabilities of the predicted structures are verified through phonon dispersion and formation energy, respectively. The electron-phonon coupling is carefully investigated by employing isotropic Eliashberg theory. The T_c values are 0.2 K, 2.3 K, and 9.0 K for Ti₂CH, Ti₂CH₂, and Ti₂CH₄, respectively. The translation and libration adopted by stretch and bent vibrations contribute to the increasing T_c of Ti₂CH₄. The high-frequency hydrogen modes contribute to the critical temperature increase. Briefly, this work not only highlights the effect of H-content on the increments of T_c for Ti₂CH_x, but also demonstrates the first theoretical evidence of the existence of H-rich MXene in the example of Ti₂CH₄. Therefore, it potentially provides a guideline for developing hydrogenated 2D superconductive applications.