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Structural, mechanical, electronic and bonding properties of TMB2 (TM = Y, Sc, Ti) under pressure: a DFT investigation

ABSTRACT Based on the first-principles calculations, we have systematically investigated the structural stability, mechanical, electronic and bonding properties of TMB2 (TM = Y, Sc, Ti) under pressure for the first time. The results show that these TMB2 (TM = Y, Sc, Ti) compounds are structurally and mechanically stable from 0 to 100 GPa. The order of hardness from high to low is TiB2 > ScB2 > YB2. Both TiB2 and ScB2 belong to the type of superhard materials at 0 GPa, but YB2 is not. These materials soften with pressure increasing, especially for ScB2, which changed from superhard to hard material at about 80 GPa. The Pugh and Poisson ratio indicated that they all have a brittle behaviour under pressure, and YB2 is more prone to ductility than ScB2 and TiB2. The bond calculation indicates that all bond lengths decrease monotonously under pressure, and the TM–B bond is more sensitive to pressure. The relationship of bond lengths for TM–B and B–B are YB2 > ScB2 > TiB2 at the same pressure, which suggests that the shorter bonds may lead to a stronger interaction between atoms. Finally, the effects of pressure on the electronic properties are also investigated in detail.