Phase diagram exploration of Tc-Al-B: From bulk Tc₂AlB₂to two-dimensional Tc₂B₂

In this study, the ternary phase diagram of the Tc-Al-B system is constructed by a combination of an evolutionary algorithm and density functional theory calculations. Four novel phases are predicted, including three binary compounds (P1̄ Al₇B₁₅,CmcmTcAl₂, andC2 TcAl₃) and one ternary compound (CmmmTc₂AlB₂). All predicted structures are mechanically, dynamically, and thermodynamically stable. Among the predicted phases,P1̄ Al₇B₁₅resembles the experimental structure of Al_0.93B₂andCmmmTc₂AlB₂corresponds to the 212-type MAB phase. Due to the in- and out-of-plane anisotropic chemical bonding inCmmmTc₂AlB₂, a tetragonal two-dimensional (2D) Tc₂B₂structure could be possibly exfoliated by chemical removal of Al atoms. The electronic structure calculations indicate that the 2D Tc₂B₂structure and its potential layered precursors are all metallic. Furthermore, the chemical reactivity of H, F, O and, OH ligands with the 2D Tc₂B₂surface is studied and the associated 2D surface-functionalized Tc₂B₂derivatives are found to be metallic. It is revealed that the F and O functional groups strengthen the surface atomic layer of 2D Tc₂B₂and enhance the Young's moduli.