Shear Strength of Superhard Transition Metal Borides under High Pressures

Adding lightweight covalently bonded boron atoms interstitially into lattices of high electron density transition metals (Re, Os) results in a unique class of materials with distinct mechanical properties and resistance to thermal degradation at high temperatures. These Transition Metal Borides boast high bulk modulus comparable to diamond (335-395 GPa) and a hardness value of 25-35 GPa. In this study, we have performed high pressure radial x-ray diffraction measurements on OsB₂, Os₂B₃, and ReB₂ to provide unique insight into the shear strength and elastic properties under non-hydrostatic compression. The radial x-ray diffraction data to pressure up to 76 GPa has been combined with the density functional theory calculations of shear modulus to obtain the variation of shear strength of transition metal borides as a function of pressure.