Compressibility, microcalorimetry, elastic properties and EELS of rhenium borides

Abstract

Based on synchrotron X-ray diffraction on phase-pure samples, we revised the bulk moduli of the rhenium borides Re7B3 (B0 (Re7B3) = 391(5) GPa) and orthorhombic Re3B (B0 (orthorhombic Re3B) = 393(4) GPa) and determined the bulk modulus of monoclinic Re3B (B0 (monoclinic Re3B) = 390(3) GPa). These results agree well with the DFT calculations on the elastic properties. Microcalorimetry was employed to obtain thermodynamic data for Re7B3 and orthorhombic Re3B and we determined Cp,298 (Re7B3) = 210(4) J/mol, ΔH2980 (Re7B3) = 40558(400) J/mol, S2980 (Re7B3) = 267(2) J/mol K and θD,298 (Re7B3) = 320(2) K, as well as Cp,298 (Re3B) = 86(1) J/mol, ΔH2980 (Re3B) = 16950(170) J/mol, S2980 (Re3B) = 112(1) J/mol K and θD,298 (Re3B) = 329(3) K. Hardness measurements were performed for Re7B3, which gave a Vickers hardness HV(5 kgf) = 14.5(4) GPa and HV(10 kgf) = 14.1(3) GPa. Electron energy loss spectroscopy (EELS) was performed on orthorhombic Re3B and ReB2, and the experimental spectra are well reproduced by theory in terms of their absorption edges.