Tantalum Diboride: The Superhard and Metallic Boride
Chuyan Cui, Jie Bi, Cheng Lü
Abstract
Understanding the intrinsic properties of metal borides is an attractive research topic in materials science. Here, we perform a computational study on the indentation shear strengths and the atomic-scale structural changes of TaB2 under indentation shear deformations based on the CALYPSO method and first-principles calculations. Abnormal strain-stiffening behaviors are found in both hexagonal P6/mmm and orthorhombic Cmmm phases of TaB2 due to the TaB12 hexagonal prisms combined with the adjacent Ta–Ta metallic bonds along the [110] direction that form a robust three-dimensional configuration, which resists the large shear deformations under Vickers indentation loading conditions. Our calculations show that the indentation shear strengths of both P6/mmm and Cmmm phases of TaB2 credibly exceed the 40 GPa threshold for superhard materials. These findings provide powerful guidelines for future experiments to synthesize and design the ideally orientated TaB2 samples and other new kinds of superhard materials.