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The pressure-induced phase transition and mechanical properties of rhenium diboride (ReB2) have been investigated by using the particle swarm optimization algorithm in combination with density functional theory calculations. It was found that the P63/mmc structure of ReB2 (hP6-ReB2) is the most stable phase at ambient conditions, and it will transform to P6/mmm structure (hP3-ReB2) at about 300.7 GPa. Phonon dispersion curve calculations suggest that hP6-ReB2 and hP3-ReB2 possess dynamical stabilities in a wide range of 0–400 and 120–400 GPa, respectively. Moreover, the calculated hardness of hP6-ReB2 is 38.1 GPa at ambient conditions, suggesting it is a potential hard material. However, hP3-ReB2 just possesses the hardness value of 18.9 GPa at the pressure of 120 GPa. Finally, by means of the quasiharmonic approximation method, the high-pressure and finite-temperature phase diagram of ReB2 is proposed. It is found that the transition pressure of hP6-ReB2 to hP3-ReB2 decreases with increasing temperatures.
Wang et al. (2019) studied this question.