Role of the A-Element in the Structural, Mechanical, and Electronic Properties of Ti 3 AC 2 MAX Phases.

Combining metallic and ceramic properties, and as precursors for MXenes, MAX phases have attracted extensive attention. In recent years, A-element substitution has been demonstrated as an effective scheme to enrich the MAX family. To explore more possible MAX members, the structural, mechanical, and electronic properties and stabilities of 31 Ti 3 AC 2 (A = Al, Si, P, S, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, Os, Ir, Pt, Au, Hg, TI, Pb, Bi, and Po) configurations are investigated in this work. Moreover, the interfacial strength implicating the possibility of exfoliating MAX into MXenes is examined. The A-element plays a crucial role in the lattice parameters and mechanical strength of Ti 3 AC 2 , and their variations are well explained by the synergistic effects of d-d and p-d hybridizations between the valence orbitals of Ti and A. Ti 3 SC 2 presents the largest Young's modulus of 360 GPa, which is 6.82% higher than that in the well-studied Ti 3 SiC 2 . Ti 3 SbC 2 is a mechanical quasi-isotropic configuration. After checking the mechanical, dynamical, and thermodynamic stability, Ti 3 AC 2 (A = Al, Si, P, S, Ga, Ge, As, Cd, In, Sn, Sb, Au, Hg, Pb, TI, and Po) are stable, while Ti 3 AC 2 (A = Fe, Co, Zn, Se, Ru, Rh, Pd, Ag, Te, Ir, Pt, and Bi) are metastable. Compared to Ti 3 AlC 2 , Ti 3 AC 2 (A = Ag, Sb, Te, Bi, and Po) exhibit much lower interfacial strength in Ti-A interfaces and larger ratios between the interfacial strengths of neighboring Ti-C and Ti-A interfaces. This implies that these configurations are promising precursors for the synthesis of Ti 3 C 2 T x (T x denotes surface groups) with a large flake size. All of the configurations are metallic, and Ti 3 AC 2 (A = Fe and Co) are magnetic. Based on the phonon dispersion and electronic structure, these Ti 3 AC 2 configurations might have potential applications in phononic crystals and topological materials.