Ordered structure and mechanical properties of ternary Sc_(0.5)TM_(0.5)B_2 (TM = Ti, V, Zr) alloys under high pressure

摘要

The structural and mechanical properties of ScB_2 and Sc_(0.5)TM_(0.5)B_2 (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 ScB_2 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 frst-principles calculations selected the stable structures of Sc_(0.5)TM_(0.5)B_2 (TM = Ti, V) and Sc0.5Zr0.5B_2 alloys as ordered structure types I and II, respectively. The formation enthalpy, phonon dispersion and elastic constants demonstrate that Sc_(0.5)TM_(0.5)B_2 (TM = Ti, V, Zr) alloys are thermodynamically, dynamically and mechanically stable. In the whole pressure range, the elastic moduli of Sc_(0.5)TM_(0.5)B_2 (TM = Ti, V, Zr) increased signifcantly compared with ScB_2. This indicates that the introduction of TM improves the mechanical properties of ScB_2. The Vickers hardness (HV) of the ScB_2 ground state is 42.4 GPa, and the H_V of the Sc_(0.5)TM_(0.5)B_2 (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 Sc_(0.5)TM_(0.5)B_2 (TM = Ti, V, Zr) alloys have stronger B-B, B-TM covalent bonds, charge interaction, and higher valence electron density, which signifcantly improves the hardness. The results show that ScB_2 and Sc_(0.5)TM_(0.5)B_2 (TM = Ti, V, Zr) alloys are potential superhard multifunctional materials.