Structural, mechanical, and thermodynamic properties of R-3m ReB4 under high pressure

The structural, mechanical, and thermodynamic properties of R-3m ReB4 under high pressure were investigated by using the density functional theory in combination with the quasi-harmonic Debye model in this work. The calculated structure parameters and bulk moduli of R-3m ReB4 at zero pressure are in good agreement with previous theoretical data. The calculated single crystal elastic constants and phonon spectra revealed that R-3m ReB4 is mechanically and dynamically stable at least 100 GPa. The pressure dependence of elastic constants and elastic modulus (B, G, and E) have been determined. Based on the obtained elastic modulus, two theoretical models were used to predict the Vickers hardness of R-3m ReB4. Furthermore, through plotting the directional dependent of bulk moduli, Young’s moduli, and shear moduli, the elastic anisotropy has been investigated in detail. Moreover, using the quasi-harmonic Debye model, some basic thermodynamical quantities such as the heat capacity, Gruneisen parameter, and the thermal expansion coefficients of R-3m ReB4 were explored under high temperature and high pressure. The obtained results can provide valuable reference for future synthesis and application R-3m ReB4 material.