Effect of chemical composition and atomic configuration on thermodynamic stability and elastic properties of AlB2-type Sc1-XVXB2 solid solutions: A first-principles investigation

As a promising candidate for hard coating, the thermodynamic stability as well as the elastic properties, of ScB2-VB2 mixtures exhibiting the AlB2-type structure are examined using a combination of the cluster-expansion method and the first-principles calculations. Our prediction reveals that, upon cooling the mixtures to low temperatures, Sc and V atoms displays a strong preference for being surrounded by atoms of the opposite type, which reside in the second coordination shell of the metal sublattice. Such a configurational preference indicates a feasibility to fabricate Sc1-XVXB2 in the form of superlattices, as described by periodic arrangements of ScB2 and VB2 layers of different thickness along the < 0001 > direction. Interestingly, the stiffness, shear strength, and hardness of Sc1-XVXB2, where 0.375 < X < 0.625, in the form either of superlattice structures or of random solid solutions show significant positive deviations from the linear Vegard's law, which can be understood in terms of the electronic band filling of the bonding states of Sc1-XVXB2. These findings also reveal that the elastic moduli and hardness of Sc1-XVXB2 are governed by the contents of ScB2 and VB2 constituting the mixtures, rather than by the atomic configuration of Sc and V.

Automated summary

This study examines the thermodynamic stability and elastic properties of ScB2-VB2 mixtures with the AlB2-type structure, which have potential as hard coatings. The research combines the cluster-expansion method and first-principles calculations to predict the behavior of the mixtures at low temperatures. The results indicate that Sc and V atoms tend to be surrounded by atoms of the opposite type, allowing for the fabrication of Sc1-XVXB2 in the form of superlattices. Interestingly, the stiffness, shear strength, and hardness of Sc1-XVXB2 deviate from Vegard's law, suggesting that the electronic band filling plays a role in their properties.