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 Re 7 B 3 ( B 0 (Re 7 B 3 ) = 391(5) GPa) and orthorhombic Re 3 B ( B 0 (orthorhombic Re 3 B) = 393(4) GPa) and determined the bulk modulus of monoclinic Re 3 B ( B 0 (monoclinic Re 3 B) = 390(3) GPa). These results agree well with the DFT calculations on the elastic properties. Microcalorimetry was employed to obtain thermodynamic data for Re 7 B 3 and orthorhombic Re 3 B and we determined C p , 298 (Re 7 B 3 ) = 210(4) J/mol, Δ H 298 0 (Re 7 B 3 ) = 40558(400) J/mol, S 298 0 (Re 7 B 3 ) = 267(2) J/mol K and θ D , 298 (Re 7 B 3 ) = 320(2) K, as well as C p , 298 (Re 3 B) = 86(1) J/mol, Δ H 298 0 (Re 3 B) = 16950(170) J/mol, S 298 0 (Re 3 B) = 112(1) J/mol K and θ D , 298 (Re 3 B) = 329(3) K. Hardness measurements were performed for Re 7 B 3 , which gave a Vickers hardness H V (5 kgf) = 14.5(4) GPa and H V (10 kgf) = 14.1(3) GPa. Electron energy loss spectroscopy (EELS) was performed on orthorhombic Re 3 B and ReB 2 , and the experimental spectra are well reproduced by theory in terms of their absorption edges.