Ordered structure and mechanical properties of ternary Sc0.5TM0.5B2 (TM = Ti, V, Zr) alloys under high pressure

Abstract

The structural and mechanical properties of ScB2 and Sc0.5TM0.5B2 (TM = Ti, V, Zr) alloys are investigated in the pressure range of 0–150 GPa based on density functional theory. The ground state structures of ScB2 are screened out by structural substitution, and the P6/mmm is determined as the initial structure of alloying research according to structural stability. The structures of alloy generation and recognition (SAGAR) code combined with first-principles calculations selected the stable structures of Sc0.5TM0.5B2 (TM = Ti, V) and Sc0.5Zr0.5B2 alloys as ordered structure types Ⅰ and Ⅱ, respectively. The formation enthalpy, phonon dispersion and elastic constants demonstrate that Sc0.5TM0.5B2 (TM = Ti, V, Zr) alloys are thermodynamically, dynamically and mechanically stable. In the whole pressure range, the elastic moduli of Sc0.5TM0.5B2 (TM = Ti, V, Zr) increased significantly compared with ScB2. This indicates that the introduction of TM improves the mechanical properties of ScB2. The Vickers hardness (HV) of the ScB2 ground state is 42.4 GPa, and the HV of the Sc0.5TM0.5B2 (TM = Ti, V, Zr) alloys are increased to 47.8, 50.3 and 44.8 GPa, respectively. The electronic structures and chemical bonding reveal that the Sc0.5TM0.5B2 (TM = Ti, V, Zr) alloys have stronger B–B, B–TM covalent bonds, charge interaction, and higher valence electron density, which significantly improves the hardness. The results show that ScB2 and Sc0.5TM0.5B2 (TM = Ti, V, Zr) alloys are potential superhard multifunctional materials.