Electronic, dynamical, and thermal properties of ultra-incompressible superhard rhenium diboride: A combined first-principles and neutron scattering study

TL;DR

This study combines first-principles calculations and neutron scattering to analyze the electronic, vibrational, and thermal properties of ultra-incompressible rhenium diboride, confirming its superhard nature and guiding future material design.

Contribution

It provides a comprehensive analysis of ReB₂'s properties using combined computational and experimental methods, validating first-principles predictions for superhard materials.

Findings

Elastic constants and hardness match experimental data

Phonon density of states agrees with neutron spectroscopy

Strong covalent B-B and Re-B bonds underlie superhardness

Abstract

Rhenium diboride is a recently recognized ultra-incompressible superhard material. Here we report the electronic (e), phonon (p), e-p coupling and thermal properties of ReB$_2$ from first-principles density-functional theory (DFT) calculations and neutron scattering measurements. Our calculated elastic constants ($c_{11}$ = 641 GPa, $c_{12}$ = 159 GPa, $c_{13}$ = 128 GPa, $c_{33}$ = 1037 GPa, and $c_{44}$ = 271 GPa), bulk modulus ($B$ $\approx$ 350 GPa) and hardness ($H$ $\approx$ 46 GPa) are in good agreement with the reported experimental data. The calculated phonon density of states (DOS) agrees very well with our neutron vibrational spectroscopy result. Electronic and phonon analysis indicates that the strong covalent B-B and Re-B bonding is the main reason for the super incompressibility and hardness of ReB$_2$. The thermal expansion coefficients, calculated within the quasi-harmonic approximation and measured by neutron powder diffraction, are found to be nearly isotropic in $a$ and $c$ directions and only slightly larger than that of diamond in terms of magnitude. The excellent agreement found between calculations and experimental measurements indicate that first-principles calculations capture the main interactions in this class of superhard materials, and thus can be used to search, predict, and design new materials with desired properties.